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Gastrointestinal Stromal Tumors With KIT Exon 9 Mutations Update on Genotype-Phenotype Correlation and Validation of a High-Resolution Melting Assay for Mutational Testing
Abstract
KIT exon 9 mutations in gastrointestinal stromal tumors (GISTs) are highly relevant and have direct therapeutic implications. In this context, we established and validated a fast and sensitive high-resolution melting assay. Analyzing 126 primary and 18 metastatic KIT exon 9-mutated cases from our registry, we demonstrate that the mutational spectrum of exon 9 is broader than previously thought and describe 3 novel mutations. Including these cases and the common p.A502_Y503dup mutation, we provide a comprehensive list of all known KIT exon 9 mutations according to the Human Genome Variation Society nomenclature. Two of the newly described mutations were associated with an aggressive phenotype and tumor progression while being treated with 400 mg imatinib, indicating that also GIST with rare exon 9 mutations could be treated with increased imatinib dosage. On the basis of >1500 GISTs from our registry, we have determined the frequency of KIT exon 9 mutations to be 9.2% among all GISTs and 22.5% among small-bowel cases. We describe for the first time that nearly 20% of exon 9-mutated GIST occur in the stomach or rectum. Furthermore, we provide first evidence that exon 9-mutated GISTs metastasize significantly more often to the peritoneum than to the liver. Performing extensive statistical analyses on data from our registry and from the literature, we demonstrate that KIT exon 9 mutations are neither associated with intermediate-risk/high-risk status nor overrepresented among metastatic lesions. Thus, we conclude that exon 9 mutations per se do not have prognostic relevance.
... KIT gene mutations are most common in KIT exon 11, followed by KIT exon 9 (3,4) . Furthermore, previous literature has proposed that siGISTs behaved more aggressively, received more emergency surgery, and showed a lower recurrence-free survival rate than that in GSTs (5,6) . ...
... The above study did not include only siGISTs because the main body of study included other sites of GISTs, such as gastric GISTs, etc., thereby affecting the accuracy and relevance of the study. Previous studies have also determined the more frequent incidence of KIT exon 9 mutations among siGISTs than that in GISTs (22.5% versus 9.2%) (4) , and demonstrated that siGISTs with KIT exon 9 have increased metastases rate and higher risk strati cation, resulting in more aggressive biological behavior and poorer prognosis. Our study evidenced that KIT exon 9 mutations were more common in patients with siGISTs than in those with GISTs or GSTs. ...
... Moreover, our study further concluded that patients with siGISTs with KIT exon 11 mutations have smaller tumor sizes, different enhancement levels, and the more likely presence of necrosis, gas, and enlarged vessels draining the tumor than the non-KIT exon 11 group. Our results partially con rm that of previous studies, which may be because siGISTs with KIT exon 11 mutations have less aggressive behavior and different morphological presence (4,16) . ...
Backgroud
This study aimed to explore the non-invasive differentiation of gene mutational subtypes of KIT exon 11 from non-KIT exon 11 in small intestinal gastrointestinal stromal tumors (siGISTs) using radiogenomics based on the contrast-enhanced CT (CECT) images.
Materials and Methods
Patients with primary siGISTs diagnosed by surgery and pathology at our hospital from May 2010 to December 2022 were retrospectively evaluated. The patients were randomly divided into a training set and a validation set with a ratio of 7:3. The synthetic minority oversampling technique algorithm was used by screening radiomics features and constructing models. Then, CECT, radiomics, and combined models are established. The performance of the three models was evaluated by the area under the curve (AUC) of the receiver operating characteristic (ROC) curve.
Results
This study included 91 siGISTs, including 59 (64.8%) with KIT exon 11 mutations and 32 (35.2%) with non-KIT exon 11 mutations. The diagnostic performance of the CECT model and radiomics model were sufficient, with the AUC values of its ROC curve being 0.746 and 0.869 in the training set, and 0.676 and 0.787 in the validation set, respectively. Additionally, the combined model composed of CECT and radiomics features has good performance, with AUC values of 0.882 (95% confidence interval [CI]: 0.828–0.937) and 0.618 (95% CI: 0.373–0.862), respectively.
Conclusions
The combined radiogenomics model based on CECT has the value of non-invasive differentiating KIT exon 11 from non-KIT exon 11 mutations in patients with siGISTs.
... KIT mutations are encountered in 75-85 % of GISTs, while 5-10 % have PDGFRA mutations [15,16]. The remainder (10-20 %) of GISTs are considered wild type (WT) and mostly carry succinate dehydrogenase (SDH), BRAF, or KRAS mutations with a relative frequency of 2, 2, and 1-5 %, respectively [15,[17][18][19][20]. KIT mutations most commonly involve exon 11 and are in the form of deletions (60-70 %) or missense mutations (20-30 %) [2]. ...
... The remainder (10-20 %) of GISTs are considered wild type (WT) and mostly carry succinate dehydrogenase (SDH), BRAF, or KRAS mutations with a relative frequency of 2, 2, and 1-5 %, respectively [15,[17][18][19][20]. KIT mutations most commonly involve exon 11 and are in the form of deletions (60-70 %) or missense mutations (20-30 %) [2]. Intestinal GISTs are usually associated with KIT exon 9 or [20][21][22]. PDGFRA mutations show high predilection to gastric epithelioid GISTs [16,23,24]. ...
... The genotype of GISTs is believed to predict patients' response to tyrosine-kinase inhibitor therapy [20,[25][26][27][28]. PDGFRA exon 18 mutant GISTs are generally resistant to imatinib therapy [16,20,25]. ...
Gastrointestinal stromal tumors (GISTs) are rare neoplasms of the gastrointestinal (GI) tract. The occurrence of these neoplasms ectopically outside the GI tract is extremely uncommon. Only one case of primary adrenal GIST has been reported in the literature. In this account, we report a second case of primary adrenal GIST in a 34-year-old male who presented with a 5-week history of gradually progressive left flank pain and early satiety. Whole-body positron emission tomography (PET)/computed tomography (CT) scan showed a 14 × 11 cm hypermetabolic 18fluorodeoxyglucose (FDG)-avid mass lesion involving the left adrenal gland and dorsal part of the left hemi-diaphragm. Biopsy of the lesion revealed tumor cells that are immunoreactive to CD-117 and CD-34 and negative to CD-31, S-100, cytokeratin, desmin, and vimentin, features characteristic of GIST. The patient was given imatinib, which drastically decreased his complaints with almost complete resolution of the tumor on his last follow-up radiographic images. Primary left adrenal GIST is an extremely rare neoplasm and can be confused with GISTs arising from the greater curvature of the stomach. Imatinib therapy is optimal in the management of these tumors.
... It is thought that the consequence of this duplication is an alteration in the receptor conformation, which mimics the binding of the physiological ligand, the stem cell factor, thus promoting constitutive activation [8] . In vitro studies have proven that mutations on KIT exon 9 reduce the sensitivity to imatinib [35] . Furthermore, presence of exon 9 mutations has been reported as the strongest adverse prognostic factor for imatinib response, and increases the relative risk of progression and death by 171% and 190% respectively, with respect to KIT exon 11 GISTs [36] . ...
... Furthermore, presence of exon 9 mutations has been reported as the strongest adverse prognostic factor for imatinib response, and increases the relative risk of progression and death by 171% and 190% respectively, with respect to KIT exon 11 GISTs [36] . Results from different studies have shown that KIT exon 9 GISTs benefit from higher dose of imatinib, with significantly better progression-free survival (PFS) [35,37,38] . For this reason, this subset of patients is treated with 800 mg per day of imatinib, (instead of 400 mg), which is now considered the standard dose for this subgroup. ...
Gastrointestinal stromal tumors (GISTs) are rare entities, which, however, represent the most common mesenchymal tumor of the gastrointestinal tract. The discovery of gain of function mutations on KIT and PDGFRA receptor genes led to a deep revolution in the knowledge of this tumor. This paved the way to the introduction of imatinib and other tyrosine-kinase inhibitors (TKIs), which terrifically revolutionized the prognosis of GIST patients. Currently, it is well established that tumor mutational status is the main player in clinical outcome; however, with the research advances, it has been slowly understood that GIST landscape is more complex than expected and the TKIs available are not effective for all the GIST subtypes. For this reason, in the era of tailored/personalized medicine, each GIST patient should be considered individually and genetic consult should be the first step to take in consideration in the therapeutic decision making process.
... The most common KIT mutations are in exon 11 and they are present in approximately 70% of the cases. Exon 9 mutations are detected in 9% of all GIST and 22% of small bowel GIST (1,2). For patients with KIT-mutated GIST, the tyrosine kinase inhibitor imatinib represents an uniquely successful targeted therapy (3), which is used both as the first-line treatment for advanced disease and as adjuvant treatment for patients at intermediate-high risk of relapse (4). ...
... Patient characteristics at baseline were compared using χ 2 of the normality assumption, the non-parametric Mann-Whitney-Wilcoxon test was used. ...
Purpose:
The effect of high-dose imatinib (800 mg/d) on survival in the adjuvant treatment of patients with resected KIT exon-9 mutated gastrointestinal stromal tumors (GIST) is not established. Here, the association of dose and other clinicopathological variables with survival was evaluated in a large multi-institutional European cohort.
Methods:
Data from 185 patients were retrospectively collected in 23 European GIST reference centers. Propensity score matching (PSM) and inverse-probability of treatment weighting (IPTW) were used to account for confounders. Univariate and multivariate unweighted and weighted Cox proportional hazard regression models were estimated for relapse-free survival (RFS), modified-RFS (mRFS) and imatinib failure-free survival (IFFS). Univariate Cox models were estimated for overall survival.
Results:
Of the 185 patients, 131 (70.8%) received a starting dose of 400 mg/d and the remaining 54 (29.2%) a dose of 800 mg/d. Baseline characteristics were partially unbalanced, suggesting a potential selection bias. PSM and IPTW analyses showed no advantage of imatinib 800 mg/d. In the weighted multivariate Cox models, high-dose imatinib was not associated to the survival outcomes (RFS: HR 1.24, 95% CI 0.79-1.94; mRFS: HR 1.69, 95% CI 0.92-3.10; IFFS: HR 1.35, 95% CI 0.79-2.28). The variables consistently associated with worse survival outcomes were high mitotic index and non-gastric tumor location.
Conclusion:
In this retrospective series of KIT exon 9-mutated GIST patients treated with adjuvant imatinib, a daily dose of 800 mg versus 400 mg did not show better results in terms of survival outcomes. Prospective evaluation of the more appropriate adjuvant treatment in this setting is warranted.
... Deletions affecting codons 557-558 of exon 11 of the c-KIT gene account to around a quarter of all GIST cases (10). KIT mutations in exon 9 (7-15% of all GIST cases) are characterized by A502-Y503 codon duplications, with up to 80% of the cases originating outside the stomach, mainly from the small intestine (11,12). The frequency of primary exon 13 and 17 mutations is around 1-2%, these tumours mostly arising from the small bowel rather than the stomach (13). ...
... In contrast to some historical observations (34) KIT exon 9 mutations per se do not have a relative (as compared with KIT exon 11 mutations of non-gastric origin) negative prognostic relevance. The worse prognosis of KIT exon 9 mutants is related to the non-gastric tumour location itself rather than to an intrinsic aggressive biologic nature of this mutation (11,14). In the meta GIST pooled analysis of two pivotal Phase III trials comparing 400 vs. 800 mg daily imatinib dose in the advanced setting, the sole predictive factor of response was the presence of KIT exon 9 mutation. ...
Gastrointestinal stromal tumours (GISTs) represent a very exciting tumour entity for the medical oncologist. There has been extensive clinical and preclinical research dissecting the natural behaviour, molecular landscape and therapeutic responsiveness of this rare mesenchymal tumour. Various molecular subtypes of GIST have a differing prognostic and predictive relevance in the state of the art management of the disease. Emerging mature clinical trial data gathered over the last one and half decade provided substantial molecular profiling information in understanding the success and eventual failure of treatment. In our review of the most relevant literature we aim to guide the clinician in tailoring neoadjuvant, adjuvant and palliative treatment of GIST alongside the different, now well established molecular subgroups of GISTs.
... für PDGFRA-Exon 18 derzeit insgesamt 60 verschiedene Mutationstypen bekannt [11]. Auch für KIT-Exon 9 ist mit 19 verschiedenen Subtypen das Mutationsspektrum größer als bisher angenommen [12]. Es ist derzeit unklar, ob alle diese Tumoren von einer erhöhten Imatinib-Dosis profitieren. ...
... [42]. Obwohl GIST mit KIT-Exon-9-Mutationen ein deutlich kürzeres progressionsfreies Überleben aufweisen, haben Exon-9-Mutationen per se keine prognostische Relevanz [12]. [46]. ...
Overview over Pathology, surgery and medical treatment in GIST as mentioned in the 10 German GIST meeting in Göttingen.
... W., H.-U. S. or R. B.). The diagnosis was based on morphology and immunohistochemistry against CD117, CD34, BCL2 (all Dako) and DOG1 (Spring Bioscience) as described previously [11,16]. The mutational status of all samples was routinely analysed by Sanger sequencing and high resolution melting analysis as described previously [5,16,17] (Table 1). ...
... The diagnosis was based on morphology and immunohistochemistry against CD117, CD34, BCL2 (all Dako) and DOG1 (Spring Bioscience) as described previously [11,16]. The mutational status of all samples was routinely analysed by Sanger sequencing and high resolution melting analysis as described previously [5,16,17] (Table 1). Two cases (case 13 and 31) showed a high polyclonal evolution of multiple secondary KIT mutations. ...
Personalised medicine and targeted therapy have revolutionised cancer treatment. However, most patients develop drug resistance and relapse after showing an initial treatment response. Two theories have been postulated; either secondary resistance mutations develop de novo during therapy by mutagenesis or they are present in minor subclones prior to therapy. In this study, these two theories were evaluated in gastrointestinal stromal tumours (GISTs) where most patients develop secondary resistance mutations in the KIT gene during therapy with tyrosine kinase inhibitors.
We used a cohort of 33 formalin-fixed, paraffin embedded (FFPE) primary GISTs and their corresponding recurrent tumours with known mutational status. The primary tumours were analysed for the secondary mutations of the recurrences, which had been identified previously. The primary tumours were resected prior to tyrosine kinase inhibitor therapy. Three ultrasensitive, massively parallel sequencing approaches on the GS Junior (Roche, Mannheim, Germany) and the MiSeqTM (Illumina, San Diego, CA, USA) were applied. Additionally, nine fresh-frozen samples resected prior to therapy were analysed for the most common secondary resistance mutations.
With a sensitivity level of down to 0.02%, no pre-existing resistant subclones with secondary KIT mutations were detected in primary GISTs. The sensitivity level varied for individual secondary mutations and was limited by sequencing artefacts on both systems. Artificial T > C substitutions at the position of the exon 13 p.V654A mutation, in particular, led to a lower sensitivity, independent from the source of the material. Fresh-frozen samples showed the same range of artificially mutated allele frequencies as the FFPE material.
Although we achieved a sufficiently high level of sensitivity, neither in the primary FFPE nor in the fresh-frozen GISTs we were able to detect pre-existing resistant subclones of the corresponding known secondary resistance mutations of the recurrent tumours. This supports the theory that secondary KIT resistance mutations develop under treatment by “de novo” mutagenesis. Alternatively, the detection limit of two mutated clones in 10,000 wild-type clones might not have been high enough or heterogeneous tissue samples, per se, might not be suitable for the detection of very small subpopulations of mutated cells.
... für PDGFRA-Exon 18 derzeit insgesamt 60 verschiedene Mutationstypen bekannt [11]. Auch für KIT-Exon 9 ist mit 19 verschiedenen Subtypen das Mutationsspektrum größer als bisher angenommen [12]. Es ist derzeit unklar, ob alle diese Tumoren von einer erhöhten Imatinib-Dosis profitieren. ...
... [42]. Obwohl GIST mit KIT-Exon-9-Mutationen ein deutlich kürzeres progressionsfreies Überleben aufweisen, haben Exon-9-Mutationen per se keine prognostische Relevanz [12]. ...
The first description of ligand-independent activating mutations in the KIT gene, which encodes the tyrosine-kinase KIT, greatly improved our understanding of gastrointestinal stromal tumour (GIST) biology. The therapeutic success in GIST has made tyrosine kinase inhibitors a "paradigm of targeted therapy". Deciphering resistance mechanisms in GIST has had implications for many other kinase-driven cancers. To exchange current knowledge within the field of GIST, the German GIST Meeting has taken place for now 10 years, traditionally in Göttingen. Subjects discussed include clinical diagnostics, pathology, surgery, and medical therapy. The following presentation gives an overview of the last meeting held in December 2013, including distinctive features in GIST and current data on the different topics.
© Georg Thieme Verlag KG Stuttgart · New York.
... Nonetheless, comparison between tumors with KIT exon 9 and KIT exon 11 mutations (both, KITdel-inc557/558 and other KIT exon 11) of nongastric origin did not show differences in tumor clinical behavior as assessed by survival analysis. Thus, we conclude that in extragastric sites, the worse prognosis of KIT exon 9 mutants is related to the tumor location rather than to an intrinsic aggressive biologic nature of this mutation, similarly to what was suggested by others (26,27). In support of this notion, the vast majority of gastric KIT exon 9 mutants in our study (6 of 7) belonged to the non-high-risk category, and only one of them progressed with relatively long DFS (56 months). ...
... PDGFRA mutations are reported in 1.6% to 2.7% of advanced GIST treated in phase III clinical trials (27,28) and up to 12.9% to 16% of primary tumors in population studies (15,16,30). In our study, PDGFRA was mutated in 14% of cases, and these mutants were almost exclusively (90.5%) of gastric origin, as previously reported (15,26,31,32). ...
Purpose:
Although the mutational status in gastrointestinal stromal tumors (GIST) can predict the response to treatment with tyrosine kinase inhibitors, the role of tumor genotype as a prognostic factor remains controversial. The ConticaGIST study sought to determine the pathologic and molecular factors associated with disease-free survival (DFS) in patients with operable, imatinib-naive GIST.
Experimental design:
Clinicopathologic and molecular data from 1,056 patients with localized GIST who underwent surgery with curative intention (R0/R1) and were registered in the European ConticaGIST database were prospectively obtained and reviewed. Risk of tumor recurrence was stratified using the modified NIH criteria. The median follow-up was 52 months.
Results:
On testing for potential prognostic parameters, the following were associated with inferior DFS on multivariable Cox model analysis: primary nongastric site, size >10 cm, mitotic index >10 mitoses per 50 high power field, and the KIT exon 9 duplication [hazard ratio (HR), 1.47; 95% confidence interval (CI), 0.9-2.5; P = 0.037] and KIT exon 11 deletions involving codons 557 and/or 558 [KITdel-inc557/558; HR, 1.45; 95% CI, 1.0-2.2; P = 0.004]. Conversely, PDGFRA exon 18 mutations were indicators of better prognosis [HR, 0.23; 95% CI, 0.1-0.6; P = 0.002]. KITdel-inc557/558 were an adverse indicator only in GIST localized in the stomach (P < 0.001) but not in tumors with nongastric origin. In gastric GIST, all other mutations presented remarkably superior 5-year DFS.
Conclusions:
In conclusion, tumor genotype is an independent molecular prognostic variable associated with gastric GIST and should be used for optimizing tailored adjuvant imatinib treatment.
... Although rare, cases of familial mastocytosis affecting two or more generations of the same family have been described, most of them are diagnosed with the cutaneous form of the disease [9][10][11][12][13]. The presence of KIT mutations in familial mastocytosis is variable and may be associated with gastrointestinal stromal tumors (GISTs) [14][15][16][17]. ...
... Genomic DNA was obtained from total BM cells, CD3 + BM cells and oral mucosa of cases 1 and 2, and from PB of all individuals using the phenol: chloroform method. Direct sequencing was performed on all coding exons of KIT (exons 1-21) and TET2 (exons 3-11), and hotspot regions of DNMT3A (exons 18-23), ASXL1 (exon 12), and SF3B1 (exons [13][14][15][16] ...
Mastocytosis are myeloproliferative neoplasms commonly related to gain-of-function mutations involving the tyrosine kinase domain of KIT. We herein report a case of familial systemic mastocytosis with the rare KIT K509I germ line mutation affecting two family members: mother and daughter. In vitro treatment with imatinib, dasatinib and PKC412 reduced cell viability of primary mast cells harboring KIT K509I mutation. However, imatinib was more effective in inducing apoptosis of neoplastic mast cells. Both patients with familial systemic mastocytosis had remarkable hematological and skin improvement after three months of Imatinib treatment, suggesting that it may be an effective front line therapy for patients harboring KIT K509I mutation.
... Mutated cases were enriched to nearly 50% in the cohort to ensure validation (see below). Immunohistochemistry was carried out in all cases as described earlier [7,11,12]. ...
... After DNA extraction, HRM analyses were performed using the LightCycler 480 platform (Roche Diagnostics, Mannheim, Germany) as described earlier [12]. Each run included PDGFRA-mutated (p.D842V) and wild-type DNA as controls. ...
The mutational status of KIT and PDGFRA is highly relevant for prognosis and therapy prediction in gastrointestinal stromal tumors (GIST). PDGFRA exon 18 mutations have direct therapeutic implications since it is crucial to distinguish mutations associated with sensitivity to tyrosine kinase inhibitors from those causing primary resistance, eg, the most common exon 18 mutation p.D842V. In response to a growing demand for reliable, faster and more sensitive methods we established and validated a high-resolution melting (HRM) assay for PDGFRA exon 18. A total of 159 GIST samples were comparatively analyzed by HRM and direct Sanger sequencing. We demonstrate that HRM provides highly reliable mutational results with higher sensitivity and shorter time to diagnosis compared to Sanger sequencing. We determined the sensitivity threshold of HRM at 6% of mutated alleles. PDGFRA exon 18 wild-type status and the most common p.D842V resistance mutation (together representing >90% of the cases) can be detected specifically by HRM. Other rare mutations can be pre-screened by HRM and afterwards determined precisely by DNA sequencing. In this way we detected four novel mutations in PDGFRA exon 18, two of which were associated with an aggressive clinical course. Including these new mutations, we provide a comprehensive overview of all 60 currently known subtypes of PDGFRA exon 18 mutations in GIST. Seven of them (accounting for about 75% of all exon 18-mutated GISTs) are reported to be resistant to imatinib. However, there are at least 10 other mutations which are regarded as sensitive to tyrosine kinase inhibitors.
... KIT exon 9 mutants were localized exclusively in the small bowel (except for one case of an unknown primary site) and were associated with spindle-cell morphology. Less common exon 9 variants have been reported in the literature, including mutations occurring in gastric and rectal locations [44]. All KIT exon 9 mutants in this study were categorized as moderate-to high-risk, with disease progression detected in five of seven cases. ...
Simple Summary
Although gastrointestinal stromal tumor (GIST) is a relatively rare mesenchymal neoplasm of the digestive tract, molecular advancements in GISTs over the past two decades have caused a paradigm shift in the field of precision oncology. GISTs are mainly driven by activating mutations in the KIT or PDGFRA oncogenes, rendering them sensitive to targeted therapies. However, there is a significant lack of data from Kuwait that needs to be addressed. We carried out this retrospective analysis of a cohort of 200 GIST patients at the Kuwait Cancer Center to provide much-needed insights into the genetic makeup and clinicopathological characteristics of our population. We detailed the mutational spectrum in KIT and PDGFRA, identified a small subgroup of wild-type tumors, and shed some light on the clinical implications. This study opens the doors for potential larger-scale, multi-institutional outcome studies in the Arabian Gulf region.
Abstract
In gastrointestinal stromal tumors (GISTs), identifying prototypical mutations in the KIT/PDGFRA oncogenes, or in rare alternate genes, is essential for prognostication and predicting response to tyrosine kinase inhibitors. Conversely, wild-type GISTs (WT-GIST), which lack known mutations, have limited treatment options. Data on the mutational landscape of GISTs and their impact on disease progression are very limited in Kuwait. Using a targeted next-generation sequencing panel, we investigated the spectrum and frequency of KIT, PDGFRA, and RAS-pathway-related mutations in 95 out of 200 GISTs diagnosed at Kuwait Cancer Center from 2005 to 2023 and assessed their correlation with clinicopathological parameters. Among the 200 tumors (median age 55 years; 15–91), 54% originated in the stomach, 33% in the small bowel, 7% in the colorectum, 1.5% in the peritoneum, and 4.5% had an unknown primary site. Of the 95 molecularly profiled cases, 88% had a mutation: KIT (61%), PDGFRA (25%), NF1 (2%), and one NTRK1 rearrangement. Ten WT-GISTs were identified (stomach = 6, small bowel = 2, and colorectum = 2). WT-GISTs tended to be smaller (median 4.0 cm; 0.5–8.0) (p = 0.018), with mitosis ≤5/5 mm², and were of lower risk (p = 0.019). KIT mutations were an adverse indicator of disease progression (p = 0.049), while wild-type status did not significantly impact progression (p = 0.934). The genetic landscape in this cohort mirrors that of global studies, but regional collaborations are needed to correlate outcomes with genetic variants.
... 6,33 Exon 9-mutated GISTs have been reported to tend more to metastasize to the peritoneum than to the liver in comparison with WT-GISTs and Exon 11-mutated GISTs. 34 Additionally, mRNA level of stem cell factor (SCF) is markedly upregulated in exon 9-mutated tumors, leading to an autocrine proliferative loop, along with overexpressed mRNAs from genes involved in the WNT pathway, 6 which has been shown to contribute to GIST malignancy. 35 Other less frequent KIT spots are in exon 13, 17, and 8 and occur in approximately 1 to 2% of KIT-GISTs. ...
Although gastrointestinal stromal tumors (GISTs) has been reported in patients of all ages, its diagnosis is more common in elders. The two most common types of mutation, receptor tyrosine kinase (KIT) and platelet-derived growth factor receptor a (PDGFRA) mutations, hold about 75 and 15% of GISTs cases, respectively. Tumors without KIT or PDGFRA mutations are known as wild type (WT)-GISTs, which takes up for 15% of all cases. WT-GISTs have other genetic alterations, including mutations of the succinate dehydrogenase and serine–threonine protein kinase BRAF and neurofibromatosis type 1. Other GISTs without any of the above genetic mutations are named “quadruple WT” GISTs. More types of rare mutations are being reported. These mutations or gene fusions were initially thought to be mutually exclusive in primary GISTs, but recently it has been reported that some of these rare mutations coexist with KIT or PDGFRA mutations. The treatment and management differ according to molecular subtypes of GISTs. Especially for patients with late-stage tumors, developing a personalized chemotherapy regimen based on mutation status is of great help to improve patient survival and quality of life. At present, imatinib mesylate is an effective first-line drug for the treatment of unresectable or metastatic recurrent GISTs, but how to overcome drug resistance is still an important clinical problem. The effectiveness of other drugs is being further evaluated. The progress in the study of relevant mechanisms also provides the possibility to develop new targets or new drugs.
... Mutations in exon 9 are almost exclusive to non-gastric GISTs and thus will not be discussed here [33]. It is worth noting that one study has claimed to observe a higher proportion of exon 9 mutations in gastric primaries, but it also deemed the mutations to not have clear prognostic implications [34]. Primary mutations in exons 13 and 17 are rare, where they are estimated to occur at a frequency of 1-2% among all GISTs, and though are they more common in the GISTs of the small bowel, they do also occur in gastric GISTs [35]. ...
Gastric gastrointestinal stromal tumors (GIST) are rare, neuroectodermal tumors primarily residing in the stomach with characteristic genetic mutations. They are often identified using ultrasound and cross-sectional imaging, or they are noted during endoscopy. Localized gastric GISTs are commonly treated with surgical resection, with the possible use of neoadjuvant or adjuvant medical therapies as they are considered to have malignant potential. The use of tyrosine kinase inhibitors (TKI) such as imatinib has been shown to successfully reduce pre-operative tumor burden, recurrence, and disease progression. Surgical resection considerations vary depending on tumor size, location, and malignant potential. Neoadjuvant and adjuvant TKI therapy dosing varies in response to the type of GIST mutation present and greatly influences prognosis. Novel cooperative minimally invasive surgical techniques and targeted therapies are currently in development to address challenges in GIST treatment for tumors in challenging locations or with significant potential for progression. The management of localized gastric GISTs continues to rapidly evolve; each case should be managed individually, where care is taken in considering details, including tumor location, tumor size, and the molecular genetic profile, before embarking on a course of treatment.
... 6 KIT exon 9 mutations are the second most common type of KIT mutation, accounting for approximately 9% of all GISTs. 7 Compared with the most common KIT exon 11 mutations, GISTs with KIT exon 9 mutations are more invasive and likely to metastasize to peritoneum and liver. [8][9][10] Previous studies have shown that imatinib is less effective in GIST patients with KIT exon 9 mutations, and their progression-free survival (PFS) and overall survival (OS) rates are short. ...
Objectives:
To establish and validate a radiomics nomogram model for preoperative prediction of KIT exon 9 mutation status in patients with gastrointestinal stromal tumors (GISTs).
Materials and methods:
Eighty-seven patients with pathologically confirmed GISTs were retrospectively enrolled in this study. Imaging and clinicopathological data were collected and randomly assigned to the training set (n = 60) and test set (n = 27) at a ratio of 7:3. Based on contrast-enhanced CT (CE-CT) arterial and venous phase images, the region of interest (ROI) of the tumors were manually drawn layer by layer, and the radiomics features were extracted. The intra-class correlation coefficient (ICC) was used to test the consistency between observers. Least absolute shrinkage and selection operator regression (LASSO) were used to further screen the features. The nomogram of integrated radiomics score (Rad-Score) and clinical risk factors (extra-gastric location and distant metastasis) was drawn on the basis of multivariate logistic regression. The area under the receiver operating characteristic (AUC) curve and decision curve analysis were used to evaluate the predictive efficiency of the nomogram, and the clinical benefits that the decision curve evaluation model may bring to patients.
Results:
The selected radiomics features (arterial phase and venous phase features) were significantly correlated with the KIT exon 9 mutation status of GISTs. The AUC, sensitivity, specificity, and accuracy in the radiomics model were 0.863, 85.7%, 80.4%, and 85.0% for the training group (95% confidence interval [CI]: 0.750-0.938), and 0.883, 88.9%, 83.3%, and 81.5% for the test group (95% CI: 0.701-0.974), respectively. The AUC, sensitivity, specificity, and accuracy in the nomogram model were 0.902 (95% confidence interval [CI]: 0.798-0.964), 85.7%, 86.9%, and 91.7% for the training group, and 0.907 (95% CI: 0.732-0.984), 77.8%, 94.4%, and 88.9% for the test group, respectively. The decision curve showed the clinical application value of the radiomic nomogram.
Conclusion:
The radiomics nomogram model based on CE-CT can effectively predict the KIT exon 9 mutation status of GISTs and may be used for selective gene analysis in the future, which is of great significance for the accurate treatment of GISTs.
... GISTs with KIT exon 11 mutations can arise anywhere in the gastrointestinal trait, although more than 80% of them occur in the stomach and are frequently larger than 2 cm at the time of diagnosis. KIT exon 9 mutations, on the other hand, are present in up to a quarter of GISTs originating in the small intestine and in 10-15% of rectal GISTs, but are rarely found in gastric GISTs [67,68]. KIT exon 13 mutant GISTs are more frequently of gastric origin, whereas exon 17 mutation occurs twice as much in small bowel compared to gastric GISTs [69]. ...
Simple Summary
GISTs are the most common mesenchymal tumors of the gastrointestinal tract. This review provides an accurate and in-depth rundown on the molecular pathways that characterize gastrointestinal stromal tumors (GISTs), together with the state of the art and future perspectives of the tailored treatment strategies studied and under investigation for this disease. The first part of this review may be a useful tool for all clinicians facing this disease in their daily clinical practice. In addition, the last chapters explore new treatment options, demonstrating encouraging preliminary results that may become the standard of care in the future.
Abstract
Gastrointestinal stromal tumors (GISTs) are one of the most common mesenchymal tumors characterized by different molecular alterations that lead to specific clinical presentations and behaviors. In the last twenty years, thanks to the discovery of these mutations, several new treatment options have emerged. This review provides an extensive overview of GISTs’ molecular pathways and their respective tailored therapeutic strategies. Furthermore, current treatment strategies under investigation and future perspectives are analyzed and discussed.
... Künstlinger et al., concluded that exon 9 mutations per se do not have a prognostic relevance as they are not associated with high risk and metastasizing tumors. 38 Data in the present study also show that KIT Exon 9 mutations, although located in the lower intestinal tract, have low risk for progression. In spite of this, caution must be taken on Exon 9 mutation. ...
Background: Gastrointestinal stromal tumors (GIST) is defined as specific, typically kit (CD117)-positive and CKIT or platelet-derived growth factor receptor alpha (PDGFRA) mutation-driven mesenchymal tumors that can occur anywhere in the GI tract. GIST diagnosis relies heavily on immunohistomorphology. However, with the advent of molecular testing, the classification, diagnosis and targeted-therapy for gastrointestinal mesenchymal tumors have been greatly improved. In the Philippines, molecular testing is not yet readily available as in other countries. The local molecular profile of gastrointestinal stromal tumors is a point of investigation as treatment may be more tailored to the patients’ needs. Objective: This study aims to determine the prevalence of CKIT and PDGFRA mutations among formalin-fixed and paraffin embedded gastrointestinal stromal tumors and other gastrointestinal mesenchymal tumors in St. Luke’s Medical Center – Quezon City. Methods: A retrospective cross-sectional study of formalin fixed and paraffin embedded tumor samples diagnosed as Gastrointestinal Stromal Tumor from January 1, 2009 to December 31, 2017 will be analyzed for KIT and PDGFRA mutations. Result: The epidemiology of GIST remains constant in that mean age group is the 5th to 6th decade, with equal gender distribution, and stomach followed by small bowel are the most common sites. Mutational analysis of the GISTs showed predominantly KIT Exon 11 (47.83%) followed by CKIT Exon 9 (13.04%) and PDGFRA Exon 18 (10.87%). For KIT Exon 11, deletion is the most common mutations followed by point mutations. No mutation is detected in 47.83% of GISTs. Conclusion: Mutational analysis for CKIT-PDGFRA is warranted among GIST patients, as it may significantly influence treatment protocol in our patients.
... Imatinib works best for c-KIT mutations in exon 11 (standard-dose imatinib), exon 9 (high-dose imatinib), and non-D842V PDGFRA mutations [28,29]. The KIT mutation A502_Y503dup comprises 90% of exon-9 mutations and is associated with locally aggressive tumors, spindle cell morphology, and decreased progression-free survival compared with exon 11 mutations, but better relapse-free survival after curative resection [30,31]. KIT exon-13 mutations are rare (1-2%) and most commonly occur as a secondary mutation after the initiation of therapy [32]. ...
Introduction:
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasm of the gastrointestinal (GI) system. Most GISTs originate from the interstitial cells of Cajal (ICC), the pacemaker cell situated between the circular and longitudinal layers of the muscularis propria along the GI tract. In this population-based study using the SEER database, we sought to identify demographic, clinical, and pathologic factors that affect the prognosis and survival of patients with this neoplasm. Molecular genetic advances, current management guidelines, and advances in targeted therapy are discussed.
Methods:
Demographic and clinical data from GIST patients were retrieved from the SEER research plus database for the period 2000-2018. Statistical analysis was performed with IBM SPSS® v20.2 software using the Chi-square test, paired t-test, multivariate analysis, and Kaplan-Meier functions.
Results:
A total of 10,833 patients with GIST were identified. Most patients were between 60-74 years of age: 40%, Caucasian: 68%, and the male to female ratio was 1.1:1. The most common primary tumor sites were stomach: 63%, small intestine: 30%, rectum: 3%, and esophagus: 0.7%. When reported, the grade of differentiation was well: 38%, moderately: 32%, undifferentiated: 19%, poorly: 12%. The size of most tumors ranged between 6-10 cm: 36% and they were treated by surgical intervention: 82% and/or chemotherapy/targeted therapy: 39%. The stage was localized: 66%, advanced: 19%, and regional: 15%. The 5-year survival was 74% (95% confidence interval (95% CI) = 72.6-74.7), and the 5-year cause-specific survival 82% (95% CI = 80.7-82.6). The 5-year cause-specific survival by treatment included surgery at 86% (95% CI = 85.4-87.3), chemotherapy/targeted therapy with or without surgery at 77% (95% CI = 75.7-78.9), and radiation at 75% (95% CI = 74.5-80). On multivariable analysis tumor size > 5 cm, poorly and undifferentiated grade, age > 60, and distant metastases at presentation were associated with worse overall survival.
Conclusion:
GISTs comprise 1-2% of malignancies of the GI tract, usually affect male Caucasians between the ages of 60 and 74 years, most tumors occur in the stomach and small intestine, and are usually >5 cm, but still localized, at the time of diagnosis. Most tumors receive multimodality surgical and chemotherapy/targeted therapy treatment, with a 5-year overall survival of 74% and cause-specific survival of 82%. GIST patients would benefit from enrollment in large clinical trials to establish better therapy guidelines for unresectable, treatment-refractory, and recurrent tumors.
... The KIT exon 9 mutations mainly occur in the non-gastric site, the clinical prognosis is worse, and a higher dose of imatinib is needed for adjuvant therapy. However, the worse prognosis of KIT exon 9 mutations is related to the location of the tumor, rather than to the intrinsically invasive biological nature of the mutation [4,35,42]. As for KIT exon 13 and exon 17, a multicenter study found that these two types of mutations were more likely to occur in the small intestine than other types of mutations; however, there was no significant difference in terms of clinical prognosis [43]. ...
Gastrointestinal stromal tumors (GISTs) are potentially malignancies that can occur anywhere in the digestive tract. Tyrosine kinase inhibitors (TKIs) such as imatinib have proven effective since the discovery of KIT and PDGFRA. The current version of NCNN, ESMO and EURACAN guidelines recognized that the three main prognostic factors are the mitotic rate, tumor size and tumor site. In addition, tumor rupture is also recognized as an independent risk factor. However, recent evidence shows that various types of gene mutations are associated with prognosis, and influencing factors such as gastrointestinal bleeding and high Ki67 index have been associated with poor prognosis. It shows that the current risk classification is still insufficient and controversial. With the emergence of more and more lack mutation in KIT/PDGFRA GISTs (KIT/PDGFRA wild-type GISTs) or drug resistance genes, primary and secondary drug resistance problems are caused, which makes the treatment of late or metastatic GIST face challenges. Therefore, this article will review the clinicopathological characteristics of GIST, the special molecular subtypes and other factors that may affect prognosis. We will also explore reliable prognostic markers for better postoperative management and improve the prognosis of patients with GIST.
... However, 75% of Japanese patients with exon 9 mutations possessed a GIST located in the stomach, and the conclusion that this mutation type is more common in the small intestine suggested by Losata et al (41) was not observed, which may be related to different ethnicities (42). Controversially, no other studies have found any association between exon 9 mutations and a poor prognosis (43). Mutation screening for exon 9 is considered to have guiding significance for GIST treatment since these claim a higher dose of imatinib to be effective, and thus also is of great significance for the treatment. ...
Gastrointestinal stromal tumors (GISTs) are the most commonly observed mesenchymal tumors of the digestive tract, and they originate from the interstitial cells of Cajal. GISTs can be divided into KIT/PDGFRA‑mutant GISTs and wild‑type GISTs based on the presence or absence of KIT/PDGFRA mutations. Wild‑type GISTs can be divided into succinate dehydrogenase complex (SDH)‑deficient GISTs and non‑SDH‑deficient GISTs. Downstream signaling pathways activated by these mutations serve a pivotal role in the development of GISTs and are associated with the biological behavior, including risk stratification, clinical prognosis and drug resistance. Accurate medical care requires accurate molecular diagnosis, which in turn prolongs the survival of patients with GISTs and makes GIST a chronic disease. At present, there is a lack of effective treatment for imatinib/sunitinib/regorafenib resistant patients and KIT/PDGFRA‑WT GISTs, which is undoubtedly a major challenge for future research. The present review summarizes the molecular pathogenesis of GISTs and the progress of related research.
... Granted, we are likely excluding most PDGFRα tumors because of their low mitotic rate. However, it is clear that many patients are not benefiting from current practice including patients with exon 9 duplication which has reduced sensitivity to the 400 mg dose of imatinib (6). ...
... They provided evidence that exon 9-mutated GISTs metastasize significantly more often to the peritoneum than to the liver. Analyzing the data of over 1500 GISTs from their registry, KIT exon 9 mutations were neither associated with intermediate-risk/high-risk status nor overrepresented among metastatic lesions and thus they concluded that exon 9 mutations per se do not have a prognostic relevance [29]. ...
Gastrointestinal stromal tumors (GISTs) are composed of various molecular subtypes, with differing prognostic and predictive relevance. Previously, tumors lacking mutations in the KIT and PDGFRA genes have been designated as 'wild-type' GISTs; however, they represent a heterogeneous group currently undergoing further subclassification. Primary and secondary resistance to imatinib poses a significant clinical challenge, therefore ongoing research is trying to evaluate mechanisms to overcome resistance. Thorough understanding of the prognostic and predictive relevance of different genetic subtypes of GIST can guide clinical decision-making both in the adjuvant and the metastatic setting. Further work is required to identify tailored therapies for specific subgroups of GISTs wild-type for KIT and PDGFRA mutations and to identify predictive factors of resistance to currently approved systemic therapies.
... 26,27 The risk of GISTs with exon 9 mutations was linked to the preferred location of this genotype in the small bowel, rather than to underlying mutation, in a recent study. 28 For example, exon 9 KIT-mutated GISTs located in the small bowel were an average size of 7cm, whereas GISTs with the same genotype mutation, but which had developed in the stomach, were an average size of 4cm. ...
Background:
The objective of the study was to investigate the relationship between molecular genetic features and the standard criteria of risk assessment in patients affected by gastrointestinal stromal tumours (GISTs).
Method:
A review was conducted of a series of 30 patients, with a mean age of 67 years, who underwent surgery for primary GISTs. R0 resection was accomplished in 27 patients. CD117, CD34 desmin, vimentin, S-100 and smooth muscle actin were immunohistochemically tested to achieve a diagnosis of GIST. The loss of wild-type KIT or platelet-derived growth factor receptor alpha (PDGFRα) genes was investigated by sequencing the tumour DNA.
Results:
Tumour genes mutations were reported in 23 patients (77%), and wild-type in seven. Mutations on the KIT gene occurred in 18 patients, and mutations on the PDGFRα gene in five. The average sizes of the GIST were 8.7 cm, 5.4 cm and 5.9 cm for KIT gene-mutated, PDGFRα gene-mutated and wild-type tumours, respectively. KIT gene mutations were detected in 50% of gastric and in 70% of extragastric GISTs. Moreover, 70% of tumours with a mitotic rate ≥ 5 x 50 highpower fi elds (HPFs) underwent KIT gene mutations. Conversely, PDGFRα mutations were observed only in gastric GISTs with a mitotic rate ≤ 5 x 50 HPFs. By stratifying GISTs according to classes of risk, KIT mutation was shown in most of the high-risk tumours. PDGFRα mutations occurred exclusively in lower classes of risk.
Conclusion:
Molecular analysis data might have a role as a prognostic variable in models of risk assessment for patients with GISTs.
... In addition, it must be remembered that mutational status is not the only prognostic factor that influences the clinical outcome of patients with GIST on receptor tyrosine kinase therapy, with initial low tumor volume, female gender, and CD34 positivity predicting higher PFS in a recent study considering patients treated with imatinib [36]. There is also evidence that exon 9mutated GIST metastasizes significantly more often to the peritoneum than to the liver and that exon 9 mutations per se may not have prognostic relevance [37]; however, we do not have the level of data required to test a possible correlation of primary KIT mutation with metastasis status and location. Another important element of the multiple mechanisms of action of sunitinib as it pertains to GIST tumor biology is the complexity of the angiogenesis process. ...
Background:
Several small studies indicated that the genotype of KIT or platelet-derived growth factor receptor-α (PDGFRA) contributes in part to the level of clinical effectiveness of sunitinib in gastrointestinal stromal tumor (GIST) patients. This study aimed to correlate KIT and PDGFRA mutational status with clinical outcome metrics (progression-free survival [PFS], overall survival [OS], objective response rate [ORR]) in a larger international patient population.
Methods:
This is a non-interventional, retrospective analysis in patients with imatinib-resistant or intolerant GIST who were treated in a worldwide, open-label treatment-use study (Study 1036; NCT00094029) in which sunitinib was administered at a starting dose of 50 mg/day on a 4-week-on, 2-week-off schedule. Molecular status was obtained in local laboratories with tumor samples obtained either pre-imatinib, post-imatinib/pre-sunitinib, or post-sunitinib treatment, and all available data were used in the analyses regardless of collection time. The primary analysis compared PFS in patients with primary KIT exon 11 versus exon 9 mutations (using a 2-sided log-rank test) and secondary analyses compared OS (using the same test) and ORR (using a 2-sided Pearson χ(2) test) in the same molecular subgroups.
Results:
Of the 1124 sunitinib-treated patients in the treatment-use study, 230 (20%) were included in this analysis, and baseline characteristics were similar between the two study populations. Median PFS was 7.1 months. A significantly better PFS was observed in patients with a primary mutation in KIT exon 9 (n = 42) compared to those with a primary mutation in exon 11 (n = 143; hazard ratio = 0.59; 95 % confidence interval, 0.39-0.89; P = 0.011), with median PFS times of 12.3 and 7.0 months, respectively. Similarly, longer OS and higher ORR were observed in patients with a primary KIT mutation in exon 9 versus exon 11. The data available were limited to investigate the effects of additional KIT or PDGFRA mutations on the efficacy of sunitinib treatment.
Conclusions:
This large retrospective analysis confirms the prognostic significance of KIT mutation status in patients with GIST. This analysis also confirms the effectiveness of sunitinib as a post-imatinib therapy, regardless of mutational status.
Trial registration:
NCT01459757.
... Whether GIST mutational data should be included in risk stratification is controversial. KIT exon 9 mutation or the mutations involving KIT exon 11 codons 557 and/or 558 are associated with a high risk of recurrence, and, on the other hand, PDGFRA mutation D842V with favourable outcome [17][18][19][20][21]. However, patients with an identical KIT or PDGFRA mutation may have widely different outcomes depending on the tumour mitotic rate suggesting that further genetic aberrations may influence the risk of recurrence more than the KIT or PDGFRA mutation [21]. ...
Patients with gastrointestinal stromal tumour (GIST) are often followed up after surgery with longitudinally repeated imaging examinations to detect recurrence early. Studies on follow-up of GIST patients are few, the optimal follow-up methods are unknown and the recommendations for follow-up vary in guidelines.
We reviewed the current evidence for follow-up of patients treated with surgery alone and of patients who were treated with adjuvant or neoadjuvant imatinib.
Imaging of the abdomen and the pelvis with computerised tomography (CT) or magnetic resonance imaging (MRI) usually suffices, since metastases are uncommon at other sites. The frequency of imaging may be adjusted with the risk of recurrence with time. Very low risk GISTs are very frequently cured with surgery and usually require no regular follow-up after complete surgery, and annual CT of the abdomen and the pelvis for 5years suffices for most patients with a low to intermediate risk for recurrence. Most high-risk patients are treated with imatinib for at least 3years after surgery. CT or MRI may be carried out 6-monthly during adjuvant imatinib, 3 to 4-monthly during the 2years that follow discontinuation of imatinib when the risk of recurrence is high, and then at 6-12month intervals to complete 10years of follow-up. Recurrence after the first 10years of follow-up is infrequent.
The follow-up schedules are best tailored with the risk of recurrence. The risk of recurrence should be estimated with the prognostic tools that consider the most relevant prognostic factors.
Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
... Zur Mutationsanalyse dient klassischerweise die Sanger-Sequenzierung; alternative Methoden sind z. B. die Pyrosequenzierung oder Schmelzpunktanalysen ("high resolution melting", HRM [18][19][20]). "Next generation sequencing" (NGS) wird bislang kaum in der Routine zur Detektion von Aberrationen verwendet, ist aber bereits in der Tumorforschung beispielsweise zur genomweiten Suche nach rekurrenten Translokationen etabliert. ...
Soft tissue tumors are often challenging for pathologists on the basis of morphology alone; therefore, tumor-specific chromosomal aberrations, such as translocations and fusions, amplifications or deletions can be diagnostically useful. Fluorescence in situ hybridization is widely used for the detection of most aberrations in routine diagnostics. Furthermore, reverse transcriptase PCR, sequencing and specific immunohistochemical assays are also applied. Next generation sequencing has already contributed to the identification of hitherto unknown aberrations. Molecular pathology is mainly used in sarcomas to discriminate between different tumor entities. In terms of personalized therapy and targeted treatment, molecular pathology can be utilized to detect predictive markers.
... Currently, either method is valid for the KIT mutation detection, particularly in gastrointestinal stromal tumors. 135 However, in our opinion, HRM is a less desirable testing methodology because it is a qualitative test; HRM data do not provide an indication of the mutated nucleotide. The molecular studies performed in previous clinical trials indicated that patients with KIT p.L576P or p.K642E mutations may respond better to targeted therapy. ...
... Primary imatinib resistance and reduced sensitivity are associated with mutations in KIT exon 17 and exon 9, PDGFRA exon 18 (D842V), and KIT/PDGFRA wild-type tumors. 4,5 Imatinib began the paradigm of molecularly based targeted solid tumor therapy, and increasingly is used as neoadjuvant therapy for borderline resectable primary or metastatic disease. 6 The molecule occupies the intracellular adenosine triphosphate binding pocket of the KIT protein and prevents substrate phosphorylation and downstream signaling, which inhibits cell proliferation. ...
Gastric gastrointestinal stromal tumors (GISTs) usually contain KIT or PDGFRA mutations that can be targeted by, or mediate resistance to, imatinib. Diagnostic material is often obtained by endoscopic ultrasound-guided fine-needle aspiration, which is often unsuitable for molecular analysis. We investigated whether targeted next-generation sequencing (NGS) can be used in multiplex genotype analysis of cytology samples collected by endoscopic ultrasound-guided fine-needle aspiration. We used the Ion AmpliSeq™ V2 Cancer Hotspot NGS Panel to identify mutations in more than 2800 exons from 50 cancer-associated genes in GIST samples from 20 patients. We identified KIT mutations in 58% of samples (91% in exon 11 and 9% in exon 17) and PDGFRA mutations in 26% (60% in exon 18, 40% in exon 12); 16% of samples had no mutations in KIT or PDGFRA. No pathogenic alterations were found in PIK3CA, BRAF, KRAS, NRAS, or FGFR3. We predicted that 32% of patients would have primary resistance to imatinib, based on mutations in exon 17 of KIT, exon 18 of PDGFRA (D842V), or no mutation in either gene. Targeted NGS of cytology samples from GISTs is feasible and provides clinically relevant data about kinase genotypes that can help guide individualized therapy.
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract, originating from Cajal's interstitial cells and accounting for approximately 80% of all primary gastric tumors. Traditional diagnostic methods for GISTs, such as computed tomography (CT), endoscopy, endoscopic ultrasound (EUS), and fine needle aspiration biopsy (FNAB), despite their widespread use, face several limitations including diagnostic uncertainty and limited biopsy capabilities. In this context, radiomics, which involves the analysis of image texture features, emerges as an innovative method potentially capable of enhancing the accuracy of GIST diagnosis. This approach allows to interpret of tissue changes through mathematical processing of images, which are imperceptible to the human eye, potentially facilitating more accurate detection of tumors at an early stage. The aim of this literature review is to evaluate the advantages and disadvantages of current diagnostic methods for GISTs, as well as to assess the potential of radiomics in improving diagnostic outcomes for these tumors. The review aims to identify the best methods of application and promising directions for future research in this important field.
Background:
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor with high prevalence of KIT and PDGFRA mutations. Few effective treatments can be exploited in imatinib or sunitinib resistant cases. While in immunotherapy, application of the highly individualized cancer neoantigen vaccines is hampered due to high economic and time cost. In this study we identified the most frequent mutation in Chinese GIST patients and predicted candidate neopeptide by next generation sequencing (NGS).
Method:
Tumor tissues and matched blood samples of 116 Chinese GIST patients were collected. Genomic profile was detected through NGS and 450 cancer genes were deeply sequenced. KIT mutations were identified and long peptides containing the mutation were queried in NetMHCpan 4.0 tools to predict MHC class I binding of mutant peptides.
Results:
The most frequent mutated genes in detected GIST patients were KIT (81.9%, 95/116), CDKN2A (18.97%, 22/116) and CDKN2B (15.52%, 18/116) in this cohort. The most common mutation of KIT was A502_Y503 duplication (15.93%, 18/113) in exon 9. Among 116 cases, 103 were HLA I genotyped and 101 were HLA II genotyped. In total, 16 samples with the mutation of KIT p.A502_Y503dup were identified to produce neoantigens with qualified HLA affinity.
Conclusion:
KIT hotspot mutation (p.A502_Y503dup) has the highest incidence, which may further eliminate the need for whole genome sequencing and patient-specific neoantigen prediction and synthesis. Therefore, for those carrying such mutation, accounting for around 16% of Chinese GIST patients, and are usually less sensitive to imatinib, effective immunotherapies are in prospect.
When gastrointestinal stromal tumour (GIST), the most common form of sarcoma, was first recognized as a distinct pathological entity in the 1990s, patients with advanced-stage disease had a very poor prognosis owing to a lack of effective medical therapies. The discovery of KIT mutations as the first and most prevalent drivers of GIST and the subsequent development of the first KIT tyrosine kinase inhibitor (TKI), imatinib, revolutionized the treatment of patients with this disease. We can now identify the driver mutation in 99% of patients with GIST via molecular diagnostic testing, and therapies have been developed to treat many, but not all, molecular subtypes of the disease. At present, seven drugs are approved by the FDA for the treatment of advanced-stage GIST (imatinib, sunitinib, regorafenib, ripretinib, avapritinib, larotrectinib and entrectinib), all of which are TKIs. Although these agents can be very effective for treating certain GIST subtypes, challenges remain and new therapeutic approaches are needed. In this Review, we discuss the molecular subtypes of GIST and the evolution of current treatments, as well as their therapeutic limitations. We also highlight emerging therapeutic approaches that might overcome clinical challenges through novel strategies predicated on the biological features of the distinct GIST molecular subtypes.
Background: The majority of gastroinstestinal stromal tumours (GISTs) harbour oncogenic mutations in the gene encoding for the tyrosine kinase KIT. The most common mutations are found in exon 11, followed by mutations in exon 9. The latter mutations are associated more frequently with GISTs in extra-gastric locations and with a more aggressive clinical behaviour.
Summary: Here, we review the unique and often poorly recognised molecular, biological and clinical characteristics that differentiate KIT exon 9-mutant GISTs from other GIST subtypes. In particular, KIT exon 9 mutations are associated to KIT mutants with retained sensitivity to stimulation by stem cell factor and localisation to the cell membrane. Moreover, KIT exon 9-mutant GISTs display significant activation of KIT-independent oncogenic pathways. These characteristics may explain the limited activity of the tyrosine kinase inhibitor imatinib in the adjuvant setting in KIT exon 9-mutant GISTs, as well as their lower sensitivity to standard dose imatinib in the advanced setting. In contranst, the multi-tyrosine kinase inhibitor sunitinib displays better activity in KIT-exon 9 mutant GISTs compared to others. Key Messages. KIT exon 9-mutant GISTs represent a subtype of GIST disctinct from others GISTs, including the more common KIT exon 11-mutant GISTs. A better understanding of the molecular biology and clinical behaviour of KIT exon 9-mutant GISTs may help identify more improved treatment options.
Purpose:
Gastrointestinal stromal tumor (GIST) arises from interstitial cells of Cajal (ICC) or their precursors, which are present throughout the gastrointestinal tract. Although gastric GIST is commonly indolent and small intestine GIST more aggressive, a molecular understanding of disease behavior would inform therapy decisions in GIST. Although a core transcription factor (TF) network is conserved across GIST, accessory TFs HAND1 and BARX1 are expressed in a disease state-specific pattern. Here, we characterize two divergent transcriptional programs maintained by HAND1 and BARX1, and evaluate their association with clinical outcomes.
Experimental design:
We evaluated RNA sequencing and TF chromatin immunoprecipitation with sequencing in GIST samples and cultured cells for transcriptional programs associated with HAND1 and BARX1. Multiplexed tissue-based cyclic immunofluorescence and IHC evaluated tissue- and cell-level expression of TFs and their association with clinical factors.
Results:
We show that HAND1 is expressed in aggressive GIST, modulating KIT and core TF expression and supporting proliferative cellular programs. In contrast, BARX1 is expressed in indolent and micro-GISTs. HAND1 and BARX1 expression were superior predictors of relapse-free survival, as compared with standard risk stratification, and they predict progression-free survival on imatinib. Reflecting the developmental origins of accessory TF programs, HAND1 was expressed solely in small intestine ICCs, whereas BARX1 expression was restricted to gastric ICCs.
Conclusions:
Our results define anatomic and transcriptional determinants of GIST and molecular origins of clinical phenotypes. Assessment of HAND1 and BARX1 expression in GIST may provide prognostic information and improve clinical decisions on the administration of adjuvant therapy.
Sarcomas are cancers arising from transformed cells of mesenchymal origin. According to the American Cancer Society 2018 statistics, about 13,040 new soft tissue sarcomas are expected to be diagnosed in the United States with 7370 cases in males and 5670 cases in females. About 5150 Americans (2770 males and 2380 females) are expected to die of soft tissue sarcomas. Sarcomas represent a genomically highly heterogenous group that in many cases share a similar clinical course. They are malignant tumors with locally aggressive growth, frequent local recurrences, or distant (mostly pulmonary) metastases. For localized disease, surgery represents the cornerstone of treatment with radiotherapy improving local control. Chemotherapy, which has been developed empirically, is greatly improving survival in bone sarcomas but is only moderately effective in some, by far not in all, soft tissue sarcoma subtypes. Targeting the underlying biology in sarcomas is beyond doubt the only measure to overcome the therapeutic standstill in the field. Predictive biomarker analyses are used to stratify patients and have come to play an enormous role in this area. This chapter will focus on predictive biomarkers in gastrointestinal stromal tumors and malignant soft tissue sarcomas. Basic principles of treatment modalities and diagnostic procedures will be covered.
Background
In 1998, Hirota et al. described the expression of a receptor tyrosine kinase of the protooncogene KIT by unique mesenchymal tumors of the gastrointestinal tract: gastrointestinal stromal tumors (GIST). Since then, molecular diagnostics have advanced, also in view of therapeutic options.
Aim
This article retraces the different tyrosine kinase receptor mutations as well as the downstream signaling pathways with subsequent nuclear events and their relevance for the prognosis and treatment of GIST.
Materials and methods
In order to answer previously unclear questions, the international literature is summarized in a structured manner.
Results
Whilst KIT is expressed in different cells (Cajal cells, hematopoietic stem cells, melanocytes, mast cells and germ cells), GIST only originate from Cajal cells (or their precursor cells); thus there should be a defined cellular context for the development of GIST. Micro-GIST already carry the driver mutation in the tyrosine kinase receptor, however, they only develop into manifest GIST if endogenous expression of the transcription factor ETV1 is high. Like KIT and PDGFRA mutations, KRAS and BRAF mutations are mutually exclusive. They can however occur as downstream mutations. Wild-type (WT) GIST with its subgroup “succinate dehydrogenase (SDH) deficiency” has to be viewed separately. Whether secondary mutations develop under therapy or are selected throughout therapy remains unclear. However, secondary mutations themselves seem to only take effect if a minimal expression level is exceeded. Therapeutic options in advanced GIST are limited because of their complex genetic evolution and the development of resistance.
Conclusions
Despite being rare, GIST remain model tumors even for complex therapeutic situations.
Background
In 1998, Hirota et al. described the expression of a receptor tyrosine kinase of the protooncogene KIT by unique mesenchymal tumors of the gastrointestinal tract: gastrointestinal stromal tumors (GIST). Since then, molecular diagnostics have advanced, also in view of therapeutic options.
Aim
This article retraces the different tyrosine kinase receptor mutations as well as the downstream signaling pathways with subsequent nuclear events and their relevance for the prognosis and treatment of GIST.
Materials and methods
In order to answer previously unclear questions, the international literature is summarized in a structured manner.
Results
Whilst KIT is expressed in different cells (Cajal cells, hematopoietic stem cells, melanocytes, mast cells and germ cells), GIST only originate from Cajal cells (or their precursor cells); thus there should be a defined cellular context for the development of GIST. Micro-GIST already carry the driver mutation in the tyrosine kinase receptor, however, they only develop into manifest GIST if endogenous expression of the transcription factor ETV1 is high. Like KIT and PDGFRA mutations, KRAS and BRAF mutations are mutually exclusive. They can however occur as downstream mutations. Wild-type (WT) GIST with its subgroup “succinate dehydrogenase (SDH) deficiency” has to be viewed separately. Whether secondary mutations develop under therapy or are selected throughout therapy remains unclear. However, secondary mutations themselves seem to only take effect if a minimal expression level is exceeded. Therapeutic options in advanced GIST are limited because of their complex genetic evolution and the development of resistance.
Conclusions
Despite being rare, GIST remain model tumors even for complex therapeutic situations.
Despite of multitude investigations no reliable prognostic immunohistochemical biomarkers in GIST have been established so far with added value to predict the recurrence risk of high risk GIST besides mitotic count, primary location and size. In this study, we analyzed the prognostic relevance of eight cell cycle and apoptosis modulators and of TP53 mutations for prognosis in GIST with high risk of recurrence prior to adjuvant treatment with imatinib. In total, 400 patients with high risk for GIST recurrence were randomly assigned for adjuvant imatinib either for one or for three years following laparotomy. 320 primary tumor samples with available tumor tissue were immunohistochemically analyzed prior to treatment for the expression of cell cycle regulators and apoptosis modulators cyclin D1, p21, p16, CDK4, E2F1, MDM2, p53 and p-RB1. TP53 mutational analysis was possible in 245 cases. A high expression of CDK4 was observed in 32.8% of all cases and was associated with a favorable recurrence free survival (RFS), whereas high expression of MDM2 (12.2%) or p53 (35.3%) was associated with a shorter RFS. These results were independent from the primary KIT or PDGFRA mutation. In GISTs with higher mitotic counts was a significantly increased expression of cyclin D1, p53 and E2F1. The expression of p16 and E2F1 significantly correlated to a non-gastric localization. Furthermore, we observed a significant higher expression of p21 and E2F1 in KIT mutant GISTs compared to PDGFRA mutant and wt GISTs. The overall frequency of TP53 mutations was low (n = 8; 3.5%) and could not be predicted by the immunohistochemical expression of p53. In summary, mutation analysis in TP53 plays a minor role in the subgroup of high-risk GIST before adjuvant treatment with imatinib. Strong expression of MDM2 and p53 correlated with a shorter recurrence free survival, whereas a strong expression of CDK4 correlated to a better recurrence free survival.
Gastrointestinal stromal tumor (GIST), the most common mesenchymal neoplasm of the gastrointestinal tract, exhibits diverse histologic and clinical manifestations. With its putative origin in the gastrointestinal pacemaker cell of Cajal, GIST can arise in association with any portion of the tubular gastrointestinal tract. Morphologically, GISTs are classified as spindled or epithelioid, though each of these subtypes encompasses a broad spectrum of microscopic appearances, many of which mimic other histologic entities. Despite this morphologic ambiguity, the diagnosis of GIST is aided in many cases by immunohistochemical detection of KIT (CD117) or DOG1 expression. The natural history of GIST ranges from that of a tumor cured by surgical resection to that of a locally advanced or even widely metastatic, and ultimately fatal, disease. This clinicopathologic heterogeneity is paralleled by an underlying molecular diversity: the majority of GISTs are associated with spontaneous activating mutations in KIT, PDGFRA, or BRAF, while additional subsets are driven by genetic lesions-often inherited-of NF1 or components of the succinate dehydrogenase enzymatic complex. Specific gene mutations correlate with particular anatomic or morphologic characteristics and, in turn, with distinct clinical behaviors. Therefore, prognostication and treatment are increasingly dictated not only by morphologic clues, but also by accompanying molecular genetic features. In this review, we provide a comprehensive description of the heterogenous molecular underpinnings of GIST, including implications for the practicing pathologist with regard to morphologic identification, immunohistochemical diagnosis, and clinical management.
The origin of gastrointestinal stromal tumors (GIST) from interstitial cells of Cajal or their precursor cells has been understood since the early 1990s. The first mutations within the KIT-gene have been described in the late 1990s. Even though these mutations were the breakthrough of small molecular therapy, we still do not know the factors responsible for their malignant transformation. Until then, we can only speak of recurrence risk. This review gives an introduction on the current understanding of GIST and highlights the remaining questions for diagnosis, tumor progression, and treatment in progressive disease.
Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors in the gastrointestinal tract although they are much less frequent than epithelial tumors. In more than 60% of cases they occur in the stomach. Especially small lesions measuring ≤1 cm in diameter, so-called microscopic GIST can occur multifocally, frequently in the proximal stomach wall and sometimes as an incidental finding in a gastrectomy specimen resected for gastric cancer. The multicentricity of GIST alone is not proof of a metastatic behavior or a syndromal or hereditary disease. Multiple sporadic synchronous and metachronous GIST are characterized by different primary mutations mostly in the KIT or PDGFRA genes and are often less aggressive. It is speculative whether a field effect is responsible or whether still unknown GIST-promoting factors may facilitate the development of several independent lesions. If KIT or PDGFRA mutations are lacking, a succinate dehydrogenase (SDH) deficient GIST has to be considered, either hereditary as Carney-Stratakis syndrome or syndromal as part of a Carney triad.
Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors with distinct clinical, morphologic, immunohistochemical, and molecular genetic features. GISTs account for 1–3 % of all gastrointestinal tumors, mainly occur in older adults, and are associated with specific KIT and PDGFRA mutations. Most GISTs immunohistochemically express KIT/CD117. GIST can involve the entire gastrointestinal tract, with a predilection for the stomach and the small intestine, whereas the liver is an uncommon primary location. Primary hepatic GISTs are well-circumscribed, firm tumors that may show central necrosis and satellite lesions. The histologic presentation corresponds to that of GISTs in other sites. Much more common than primary hepatic GIST are metastatic lesions, the liver being one of the most common metastatic sites of gastric and intestinal GIST. Liver metastases of GIST can undergo a distinct cystic change upon therapy with imatinib. Radiologically, part of these cysts closely mimic simple nonparasitic liver cysts.
Numerous types of KIT mutations have been reported in gastrointestinal stromal tumors (GISTs); however, controversy still exists regarding their clinicopathological significance. In this study, we reviewed the publicly available literature to assess the data by a meta-analysis to characterize KIT mutations and different types of KIT mutations in prognostic prediction in patients with GISTs. Twenty-eight studies that included 4,449 patients were identified and analyzed. We found that KIT mutation status was closely correlated with size of tumors and different mitosis indexes, but not with tumor location. KIT mutation was also observed to be significantly correlated with tumor recurrence, metastasis, as well as the overall survival of patients. Interestingly, there was higher risk of progression in KIT exon 9-mutated patients than in exon 11-mutated patients. Five-year relapse-free survival (RFS) rate was significantly higher in KIT exon 11-deleted patients than in those with other types of KIT exon 11 mutations. In addition, RFS for 5 years was significantly worse in patients bearing KIT codon 557–558 deletions than in those bearing other KIT exon 11 deletions. Our results strongly support the hypothesis that KIT mutation status is another evaluable factor for prognosis prediction in GISTs.
Background & aims:
In an era of precision medicine, customized genotyping of gastrointestinal stromal tumors by screening for driver mutations will become the standard of care. The fidelity of genotype concordance between paired cytology smears and surgical pathology specimens is unknown. In patients with either primary or metastatic sporadic disease, we sought to determine the frequency of KIT and PDGFRA pathogenic alterations within such specimens, imatinib sensitivity and the concordance of pathogenic alterations between paired specimens.
Methods:
DNA obtained from cytology smears from 36 patients, 24 of whom had paired surgical pathology specimens, underwent targeted next generation sequencing using a custom panel to evaluate somatic mutations within KIT (Exon 2, 9, 10, 11, 13, 14, 15, 17, 18) and PDGFRA (Exon 12, 14, 15, 18) genes. KIT and PDGRFA wild-type patients completed the Qiagen™ Human Comprehensive Cancer GeneRead DNAseq Targeted Array V2.
Results:
Genotyping revealed KIT and PDGFRA mutations in 68% and 15% of patients. The wild-type population did not harbor mutations in BRAF, RAS family, SDHB, SETD2 or NF1. Imatinib sensitivity based on the oncogenic kinase mutation prevalence was estimated to be 68%. Mutational concordance between paired cytology and surgical pathology specimens was 96%.
Conclusions:
Our data have demonstrated the ability to stratify either primary or metastatic gastrointestinal stromal tumors by mutational subtype using two targeted next generation sequencing gene mutation panels. We highlight the ability to use cytology specimens obtained via minimally invasive techniques as a surrogate to surgical specimens given the high mutational landscape concordance between paired specimens.
Histone deacetylases (HDAC) are key players in epigenetic regulation of gene expression and HDAC inhibitor (HDACi) treatment seems to be a promising anti-cancer therapy in many human tumours, including soft tissue sarcomas. HR23b has been shown to be a potential biomarker for sensitivity to HDACi therapy in cutaneous T-cell lymphoma and hepatocellular carcinoma. We aimed to evaluate HR23b as a candidate biomarker for HDACi response in sarcomas and gastrointestinal stromal tumours (GIST). Therefore, HR23b expression was analysed comprehensively by Western blot in sarcoma and GIST cell lines covering all major clinically relevant subtypes. MTT assay and ApoTox-GloTM Triplex assay were performed after treatment with vorinostat, belinostat, mocetinostat and entinostat. HR23b protein expression was measured under HDACi treatment. Furthermore, HR23b expression levels were immunohistochemically determined in a large set of 523 clinical samples from sarcoma and GIST patients. Western blot analyses showed that sarcomas differ significantly in their expression of HR23b protein. All HDACi were able to regulate proliferation and apoptosis in vitro. Sensitivity to vorinostat correlated significantly with HR23b protein expression. Immunohistochemical prevalence screening in clinical samples of relevant adult-type tumours revealed that 12.5% of sarcomas (among them malignant peripheral nerve sheath tumours, pleomorphic liposarcomas, leiomyosarcomas, dedifferentiated liposarcomas, synovial sarcomas and angiosarcomas) and 23.2% of GIST show high HR23b expression. Therefore, HDACi have antiproliferative and proapoptotic effects in sarcomas depending on the expression level of HR23b. These findings suggest that HR23b represents a candidate biomarker for HDACi sensitivity in certain sarcoma types and in GIST. This article is protected by copyright. All rights reserved.
Gastrointestinal stromal tumors (GISTs) are the most spread mesenchymal tumors located within the gastrointestinal tract that have particular clinico-morphological, immunohistochemical and molecular characteristics. The distinguishing mark of GISTs is the presence of the cell-surface antigen CD117 (KIT receptor tyrosine kinase), identified by immunohistochemistry. GISTs consist of tumors with various activating mutations in KIT (75–80 %) or PDGFRA (5–15 %) receptor tyrosine kinases. Numerous KIT and PDGFRA mutations are associated with specific GIST morphology, histologic phenotype, metastasizing and prognosis. 10–15 % of GISTs contain KIT and PDGFRA wild type genes, some of them have driver BRAF, IGF1R or PIK3CA mutations. The other GISTs patients have familial syndromes (neurofibromatosis type 1, Carney–Stratakis syndrome, Carney triad) and contain germline mutations of NF1 or the genes coding for the succinate dehydrogenase subunits SDHA, SDHB, SDHC, and SDHD. GISTs are first and the most studied model for development of principles and methods of personalized targeted therapy of solid tumors with tyrosine kinase inhibitors.
Many types of KIT mutations have been observed in gastrointestinal stromal tumors (GISTs), but their prognostic and predictive significance are still unclear. A meta-analysis and literature review were conducted to estimate the contribution of KIT mutations in prognostic parameters and clinic-pathological significance of GISTs. A total of 18 relevant articles from PubMed, EMBASE and Web of Science databases were included in this study. The frequency of KIT mutation was significantly increased in the GIST patients with higher mitosis (≥5/50 high-power fields (HPFs) and larger size (≥5 cm) of tumors than in those with lower MI (≤5/50HPFs) and smaller size (≤5 cm) of GISTs respectively. The rate of KIT mutation was not significantly changed between GISTs in stomachs and in small intestines. KIT mutational status has prognostic significance for patients' outcome. GIST patients with KIT exon 9 mutations have higher risk of progression than those with exon 11 mutations. 5 year relapse-free survival (RFS) rate was significantly higher in patients with KIT exon 11 deletion than in those with other type of KIT exon 11 mutations. The deletion involving KIT exon 11, particularly codons 557-558, is a valuable predictor of prognosis for patients with GISTs.
Approximately 85-90% of adult gastrointestinal stromal tumors (GISTs) harbor KIT and PDGFRA mutations. The remaining cases, including the majority of pediatric GISTs, lack these mutations, and have been designated as KIT/PDGFRA wild-type (WT) GISTs. Nearly 15% of WT GISTs harbor BRAF mutations, while others arise in patients with type I neurofibromatosis. Recent work has confirmed that 20-40% of KIT/PDGFRA WT GISTs show loss of function of succinate dehydrogenase complex. Less than 5% of GISTs lack known molecular alterations ("quadruple-negative" GISTs). Thus, it is important to consider genotyping these tumors to help better define their clinical behavior and therapy.
Copyright © 2015 Elsevier Inc. All rights reserved.
Mutated KIT and platelet-derived growth factor alpha gene (PDGFRA) drive GI stromal tumor (GIST) oncogenesis, but the clinical significance of their single mutations is known incompletely.
We identified 11 population-based series of patients with GIST through a literature search and pooled individual data from 3,067 patients treated with macroscopically complete tumor excision. Mutation analysis was done from 1,505 tumors. We analyzed associations between KIT and PDGFRA mutations and recurrence-free survival (RFS) in the subsets in which patients were treated with surgery alone.
We identified 301 different single mutations in KIT and 33 in PDGFRA. Patients with PDGFRA mutations had more favorable RFS than those with KIT mutations (hazard ratio, 0.34; P = .004). Only one of the 35 GISTs with KIT exon 11 duplication mutations recurred. Patients with deletions of only one codon of KIT exon 11 had better RFS than those with another deletion type, and some KIT exon 11 substitution mutations (Trp557Arg, Val559Ala, and Leu576Pro) were also associated with favorable RFS. Patients with an identical mutation had greatly variable outcomes depending on the standard prognostic factors, notably, mitotic count. Commonly used risk stratification schemes tended to overestimate the risk for recurrence in subgroups with prognostically favorable mutations.
GISTs with an identical KIT or PDGFRA mutation may have widely varying risks for recurrence. Most of the patients with PDGFRA mutations and those with KIT exon 11 duplication mutation or deletion of one codon have favorable RFS with surgery alone and are usually not candidates for adjuvant therapy.
© 2015 by American Society of Clinical Oncology.
About 10-15% of gastrointestinal stromal tumors (GISTs) carry wild-type sequences in all hot spots of KIT and platelet-derived growth factor receptor alpha (PDGFRA) (wt-GISTs). These tumors are currently defined by having no mutations in exons 9, 11, 13, and 17 of the KIT gene and exons 12, 14, and 18 of the PDGFRA gene. Until now, the analysis of further exons is not recommended. However, we have previously published a report on a KIT exon 8 germline mutation, which was associated with familial GIST and mastocytosis. We therefore investigated whether KIT exon 8 mutations might also occur in sporadic GIST. We screened a cohort of 145 wt-GISTs from a total of 1351 cases from our registry for somatic mutations in KIT exon 8. Two primary GISTs with an identical exon 8 mutation (p.D419del) were detected, representing 1.4% of all the cases analyzed. Based on all GISTs from our registry, the overall frequency of KIT exon 8 mutations was 0.15%. The first tumor originating in the small bowel of a 53-year-old male patient had mostly a biphasic spindled-epithelioid pattern with a high proliferative activity (14 mitoses/50 HPF) combined with a second low proliferative spindle cell pattern (4/50 HPF). The patient developed multiple peritoneal metastases 29 months later. The second case represented a jejunal GIST in a 67-year old woman who is relapse-free under adjuvant imatinib treatment. We conclude that about 1-2% of GISTs being classified as 'wild type' so far might, in fact, carry KIT mutations in exon 8. Moreover, this mutational subtype was shown to be activating and imatinib sensitive in vitro. We therefore propose that screening for KIT exon 8 mutations should become a routine in the diagnostic work-up of GIST and that patients with an exon 8 mutation and a significant risk for tumor progression should be treated with imatinib.Modern Pathology advance online publication, 19 April 2013; doi:10.1038/modpathol.2013.47.
The risk of recurrence of gastrointestinal stromal tumour (GIST) after surgery needs to be estimated when considering adjuvant systemic therapy. We assessed prognostic factors of patients with operable GIST, to compare widely used risk-stratification schemes and to develop a new method for risk estimation.
Population-based cohorts of patients diagnosed with operable GIST, who were not given adjuvant therapy, were identified from the literature. Data from ten series and 2560 patients were pooled. Risk of tumour recurrence was stratified using the National Institute of Health (NIH) consensus criteria, the modified consensus criteria, and the Armed Forces Institute of Pathology (AFIP) criteria. Prognostic factors were examined using proportional hazards and non-linear models. The results were validated in an independent centre-based cohort consisting of 920 patients with GIST.
Estimated 15-year recurrence-free survival (RFS) after surgery was 59·9% (95% CI 56·2-63·6); few recurrences occurred after the first 10 years of follow-up. Large tumour size, high mitosis count, non-gastric location, presence of rupture, and male sex were independent adverse prognostic factors. In receiver operating characteristics curve analysis of 10-year RFS, the NIH consensus criteria, modified consensus criteria, and AFIP criteria resulted in an area under the curve (AUC) of 0·79 (95% CI 0·76-0·81), 0·78 (0·75-0·80), and 0·82 (0·80-0·85), respectively. The modified consensus criteria identified a single high-risk group. Since tumour size and mitosis count had a non-linear association with the risk of GIST recurrence, novel prognostic contour maps were generated using non-linear modelling of tumour size and mitosis count, and taking into account tumour site and rupture. The non-linear model accurately predicted the risk of recurrence (AUC 0·88, 0·86-0·90).
The risk-stratification schemes assessed identify patients who are likely to be cured by surgery alone. Although the modified NIH classification is the best criteria to identify a single high-risk group for consideration of adjuvant therapy, the prognostic contour maps resulting from non-linear modelling are appropriate for estimation of individualised outcomes.
Academy of Finland, Cancer Society of Finland, Sigrid Juselius Foundation and Helsinki University Research Funds.
Mutation analysis of KIT and PDGFRA genes in gastrointestinal stromal tumors is gaining increasing importance for prognosis of GISTs and for prediction of treatment response. Several groups have identified specific mutational subtypes in KIT exon 11 associated with an increased risk of metastatic disease whereas GISTs with PDGFRA mutations often behave less aggressive. Furthermore, in advanced GIST disease with proven KIT exon 9 mutation the doubled daily dose of 800 mg imatinib increases the progression free survival and is now recommended both in the European and the American Guidelines. In Germany, there are still no general rules how to perform mutational analysis.
When comparing results from six different molecular laboratories we recognized the need of standardisation. Six German university laboratories with experience in mutation analysis in GISTs joined together to develop recommendations for the mutation analysis of the most common and clinically relevant hot spots, i. e. KIT exons 9 and 11 and PDGFRA exon 18. We performed a three-phased interlaboratory trial to identify pitfalls in performing molecular analysis in GISTs.
We developed a design for a continuous external laboratory trial. In 2009 this external trial was conducted by 19 laboratories via the initiative for quality assurance in pathology (QuiP) of the German Society of Pathology and the Professional Association of German Pathologists.
By performing a three-phased internal interlaboratory trial and conducting an external trial in Germany we were able to identify potential pitfalls when performing KIT and PDGFRA mutational analysis in gastrointestinal stromal tumors. We developed standard operation procedures which are provided with the manuscript to allow other laboratories to prevent these pitfalls.
KRAS mutations can be detected in approximately 30% to 40% of all patients with colorectal cancer. Several recent studies have shown that patients with KRAS mutations in codons 12 or 13 in metastatic tumors do not benefit from anti-epidermal growth factor receptor therapy with cetuximab or panitumumab.
To review the literature on the role of KRAS mutation testing for management of patients with metastatic colorectal cancer and to discuss testing strategies.
This review is based on published, peer-reviewed literature; available information from medical organizations (eg, National Comprehensive Cancer Network, American Society of Clinical Oncology, College of American Pathologists); and information from clinical laboratories conducting KRAS mutation analysis.
Multiple methods for detecting KRAS mutations in colorectal tumors are available, and all methods in current clinical use appear to have adequate clinical sensitivity for predicting a lack of response to cetuximab and panitumumab. Pathologist expertise is essential to quality KRAS testing and to determining effective treatment for patients with metastatic colorectal cancer.
Gastrointestinal stromal tumors (GIST) are commonly regarded as solitary tumors. The occurrence of multiple lesions is considered an extraordinary event restricted to pediatric GISTs and rare hereditary conditions. Beyond these well-defined situations, the presentation of multiple synchronous lesions is commonly viewed as the result of the metastatic spreading of a single primary GIST. Based on this axiom, patients with multifocal disease are classified as advanced stage and treated as such. Whether, indeed, the detection of several lesions in sporadic adult GIST patients may be suggestive of phenomena of tumor multiplicity still needs to be clarified.
From a multicentric series of 442 consecutive cases, 26 of which with advanced disease, we selected 5 patients who presented up to three distinct GIST nodules. Five additional cases with similar characteristics were also contributed by two other institutions. The clonal relationship between the synchronous lesions was assessed by comparing KIT/PDGFRA mutation and microsatellite pattern.
An independent origin of the synchronous lesions was established in 6 of 10 cases. Notably, in one patient, one lesion arose in the peritoneum, which is ordinarily regarded as a site of metastasis.
Our data indicate that a significant fraction of GIST patients with multifocal presentation are actually affected by multiple primary tumors, suggesting that mesenchymal GIST precursor cells of these individuals are somehow primed to transformation. Thus, in the presence of multifocal GIST manifestations, an accurate characterization of the different tumor sites should be undertaken for a proper patient staging and therapy planning.
Gastrointestinal stromal tumors (GISTs) commonly harbor oncogenic mutations of the KIT tyrosine kinase, which is a target for the kinase inhibitor imatinib. A subset of GISTs, however, contains mutations in the homologous kinase platelet derived growth factor receptor alpha (PDGFRA), and the most common of these mutations is resistant to imatinib in vitro. Little is known of the other types of PDGFRA mutations that occur in GISTs.
We determined the KIT and PDGFRA mutation status of 1,105 unique GISTs using a combination of denaturing high-performance liquid chromatography and direct sequencing.
66 in exon 18, 11 in exon 12, and three in exon 14. Transient expression of representative PDGFRA isoforms in CHO cells revealed imatinib sensitivity of exon 12 mutations (SPDHE566-571R and insertion ER561-562) and an exon 14 substitution (N659K). However, most isoforms with a substitution involving codon D842 in exon 18 (D842V, RD841-842KI, DI842-843IM) were resistant to the drug, with the exception of D842Y. Interestingly, other mutations in exon 18 (D846Y, N848K, Y849K and HDSN845-848P) were all imatinib sensitive. Proliferation studies with BA/F3 cell lines stably expressing selected PDGFRA mutant isoforms supported these findings.
Including our cases, there are 289 reported PDGFRA-mutant GISTs, of which 181 (62.6%) had the imatinib-resistant substitution D842V. However, our findings suggest that more than one third of GISTs with PDGFRA mutations may respond to imatinib and that mutation screening may be helpful in the management of these tumors.
The aim of the current study was to examine the prognostic relevance of the CDKN2A tumor suppressor pathway in gastrointestinal stromal tumors (GIST).
We determined the mRNA expression of p1(INK4A), p14(ARF), CDK4, RB1, MDM2, TP53, and E2F1 by quantitative reverse transcription-PCR in 38 cases of GISTs and correlated the findings with clinicopathologic factors, including mutation analysis of KIT and PDGFRA.
The k-means cluster analysis yielded three prognostic subgroups of GISTs with distinct mRNA expression patterns of the CDKN2A pathway. GISTs with low mRNA expression of the CDKN2A transcripts p16(INK4A) and p14(ARF) but high mRNA expression of CDK4, RB1, MDM2, TP53, and E2F1 were associated with aggressive clinical behavior and unfavorable prognosis, whereas GISTs with a low mRNA expression of CDK4, RB1, MDM2, TP53, and E2F1 were not. GISTs with a moderate to high mRNA expression of all examined genes also seemed to be associated with unfavorable prognosis. Regarding mutation analysis, we found significant differences in the KIT/PDGFRA genotype among the three clusters. Univariate analysis revealed high expression of E2F1 to be associated with mitotic count, proliferation rate, KIT mutation, and aggressive clinical behavior. These findings on mRNA level could be confirmed by immunohistochemistry.
Our findings implicate differential regulation schemes of the CDKN2A tumor suppressor pathway converging to up-regulation of E2F1 as the critical link to increased cell proliferation and adverse prognosis of GISTs.
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of gastrointestinal tract. GISTs range from benign indolent neoplasms to highly malignant sarcomas. Gain-of-function mutations of tyrosine kinase receptors, KIT or PDGFRA, have been identified in most GISTs. In this study, we report 36 GIST patients whose tumors had homozygous KIT exon 11 mutations detected by direct sequencing of PCR products. Loss of heterozygosity in KIT locus and other chromosome 4 loci were documented in majority of these tumors. However, fluorescence in situ hybridization with KIT locus-specific probe and chromosome 4 centromeric enumeration probe showed no evidence of KIT hemizygosity in a majority of analyzed cases. These findings are consistent with duplication of chromosome 4 with KIT mutant allele. Homozygous KIT exon 11 mutations were found in 33 primary tumors and 7 metastatic lesions. In two cases, shift from heterozygosity to homozygosity was documented during tumor progression being present in metastases, but not in primary tumors. Among primary GISTs, there were 16 gastric, 18 intestinal and 2 from unknown locations. An average primary tumor size was 12 cm and average mitotic activity 32/50 HPFs. Out of 32 tumors 29 (90.6%) with complete clinicopathologic data were diagnosed as sarcomas with more than 50% risk of metastatic disease, and 26 of 29 patients with follow-up had metastases or died of disease. An average survival time among pre-imatinib patients, who died of the disease was 33.4 months. Based on these findings, we conclude that presence of homozygous KIT exon 11 mutations is associated with malignant course of disease and should be considered an adverse prognostic marker in GISTs.
To assess KIT and PDGFRA mutations frequencies in a Portuguese series of gastrointestinal stromal tumours (GISTs).
78 GISTs were evaluated for CD117 expression and screened for mutations in KIT (exons 9, 11, 13, 14 and 17) and PDGFRA (exons 12, 14 and 18) genes.
KIT activating mutations were identified in 44 (56%) of the 78 GISTs. Forty cases (91%) presented a mutation in KIT exon 11, and 4 (9%) in exon 9. One case showed a 4 bp deletion in intron 14. PDGFRA mutations were observed in 5 cases (6%): 2 (3%) in exon 12 and 3 (4%) in exon 18. Survival analysis was performed in 63 of the 78 GISTs. The presence of mutated KIT was significantly correlated with shorter survival of patients (p = 0.0460), and inversely associated with epithelioid histological type of GISTs (p = 0.0064).
Overall, the incidence of both KIT and PDGFRA mutations in these Portuguese series was 63%, being in agreement with other studies, mainly of Iberian populations. The great majority of mutations were located in KIT exon 11, statistically associated with worse prognosis and indicative of favourable response to imatinib-based therapy in this Portuguese series of GISTs.
Gastrointestinal stromal tumors (GISTs) are mesenchymal neoplasms driven by oncogenic, mutational activation of KIT or platelet-derived growth factor receptor alpha (PDGFRA). GIST-specific KIT or PDGFRA mutations have been linked to tumor location, tumor cell morphology and clinical behavior. The purpose of this study was to evaluate the clinicopathologic profile of GISTs that have KIT exon 13 or exon 17 mutations. Through the collaboration of several GIST research groups, we gathered 54 cases from the pre-imatinib era that had such primary mutations. From our observations and those in the literature, we estimate that the frequency of these mutations is no higher than 1-2%. Almost all (32 of 33, 97%) of the KIT exon 13 mutations were the 1945A>G substitution leading to Lys642Glu. A majority (15 of 21, 71.4%) of the KIT exon 17 mutations were the 2487T>A substitution leading to Asn822Lys. Demographic and clinicopathologic data were available for 26 and 14 KIT exon 13 and exon 17 mutant GISTs, respectively. Median age and male to female ratio were similar to ones reported in other GIST studies. Small intestinal tumors were two times more frequent than gastric ones among KIT exon 17 mutants. Also, intestinal tumors were slightly overrepresented among KIT exon 13 mutants when compared with population-based studies. The majority of KIT exon 13 or exon 17 mutants had a spindle-cell morphology and only a few had epithelioid features. Tumor size varied from 1.2 to 25 cm and average mitotic rates were 9.5 and 4.2 for KIT exon 13 and exon 17 mutants, respectively. Gastric KIT exon 13 mutant GISTs tend to be slightly larger and more aggressive than gastric GISTs in average, whereas the behavior of small intestinal GISTs with KIT exon 13 mutations does not differ from other small intestinal GISTs. The latter is also true for all KIT exon 17 mutant GISTs.
To study the association of the frequency and pattern of KIT and PDGFRA mutations and clinicopathological factors in a group of patients with gastrointestinal stromal tumors (GIST).
Thirty patients with GIST were examined. Exons 9, 11, 13, and 17 of the KIT and exons 12 and 18 of the PDGFRA gene were analyzed for the presence of mutations by PCR amplification and direct sequencing.
KIT or PDGFRA mutations were detected in 21 of the 30 patients (70%). Sixteen patients had mutations within KIT exon 11, three within KIT exon 9, and two within PDGFRA exon 18. GISTs with KIT exon 9 mutations were predominantly located in the small intestine, showed a spindle cell phenotype, and were assessed as potentially malignant. GISTs with KIT exon 11 mutations were located in the stomach and intestine, showed mainly a spindle cell phenotype, and were scored as potentially malignant (P < 0.05). Tumors with KIT exon 11 codon 557/558 deletion/insertion mutations were found to be associated with a potentially malignant clinical behaviour (P < 0.003). GISTs with PDGFRA mutations located in stomach showed a mixed cell phenotype and were classified as of very low or low moderate malignant potential.
Determination of KIT and PDGFRA mutations should be additional parameters for the better prediction of GISTs clinical behaviour. Tumors with deletion/insertion mutations affecting codons 557/558 of the KIT gene seem to represent a distinct subset of malignant GISTs.
The major changes to the 2012 and 2011 NCCN Guidelines for Soft Tissue Sarcoma pertain to the management of patients with gastrointestinal stromal tumors (GISTs) and desmoid tumors (aggressive fibromatosis). Postoperative imatinib following complete resection for primary GIST with no preoperative imatinib is now included as a category 1 recommendation for patients with intermediate or high risk of recurrence. The panel also reaffirmed the recommendation for preoperative use of imatinib in patients with GISTs that are resectable with negative margins but associated with significant surgical morbidity. Observation was included as an option for patients with resectable desmoid tumors that are small and asymptomatic, not causing morbidity, pain, or functional limitation. Sorafenib is included as an option for systemic therapy for patients with desmoid tumors. (JNCCN 2012;10:951-960)
Gastrointestinal (GI) stromal tumors (GISTs), the specific KIT- or PDFGRA-signaling driven mesenchymal tumors, are the most common mesenchymal tumors of the GI tract. This study analyzed 1091 tumors originally classified as smooth muscle tumors of the small intestine (including jejunum or ileum and excluding duodenum), and found that 906 (83%) of these were GISTs. The GIST patients had 55:45 male-to-female ratio with a median age of 59 years (range, 13–94 years). Only 0.6% of tumors occurred before the age of 21 years and 13.6% before the age of 40 years. The tumors varied from 0.3 to 40 cm (median, 7.0 cm) and most commonly presented with GI bleeding or acute abdomen; 18% were incidentally detected. Histologically, the tumors were relatively monotypic with spindle cell (86%), epithelioid (5%), or mixed patterns (9%). Skeinoid fibers were present in 44% of cases, and their presence was associated with a favorable course. Most epithelioid tumors were malignant, and this morphology sometimes emerged from less cellular and less mitotically active spindle cell tumors, suggesting that it represented a transformation. KIT was immunohistochemically detected in 98%, CD34 in 40%, smooth muscle actin in 34%, desmin in 0.2%, and S-100 protein in 14% of the tumors tested. Outcome was strongly dependent on tumor size and mitotic activity, with an overall 39% tumor-related mortality, twice that for gastric GISTs. Only <3% of tumors <5 cm and ≤5 mitoses/50 HPF metastasized, whereas 86% of tumors >10 cm and >5 mitoses/50 HPF metastasized. In stark contrast to corresponding gastric tumors, tumors >10 cm with mitotic activity ≤5/50 HPF and those ≤5 cm with mitoses >5/50 HPF had a high metastatic rate (>50%); tumors >5 cm ≤10 cm with low mitotic rate had a 24% metastatic rate. The median survival times of patients with low mitotic rate tumors who died of disease decreased by increasing tumor size. KIT exon 11 mutations were detected in 90 cases, exon 9 mutation in 17 cases, and exon 17 mutation in 1 case; the presence of mutation or mutation type was not prognostically significant. There were no PDGFRA exon 12 or 8 mutations. Systematic data on prognosis of small intestinal GISTs of various size and mitotic activity categories can be helpful in management and surveillance of patients with these tumors.
AIM: To study the association of the frequency and pattern of KIT and PDGFRA mutations and clinicopathological factors in a group of patients with gastrointestinal stromal tumors (GIST).
METHODS: Thirty patients with GIST were examined. Exons 9, 11, 13, and 17 of the KIT and exons 12 and 18 of the PDGFRA gene were analyzed for the presence of mutations by PCR amplification and direct sequencing.
RESULTS: KIT or PDGFRA mutations were detected in 21 of the 30 patients (70%). Sixteen patients had mutations within KIT exon 11, three within KIT exon 9, and two within PDGFRA exon 18. GISTs with KIT exon 9 mutations were predominantly located in the small intestine, showed a spindle cell phenotype, and were assessed as potentially malignant. GISTs with KIT exon 11 mutations were located in the stomach and intestine, showed mainly a spindle cell phenotype, and were scored as potentially malignant (P < 0.05). Tumors with KIT exon 11 codon 557/558 deletion/insertion mutations were found to be associated with a potentially malignant clinical behaviour (P < 0.003). GISTs with PDGFRA mutations located in stomach showed a mixed cell phenotype and were classified as of very low or low moderate malignant potential.
CONCLUSION: Determination of KIT and PDGFRA mutations should be additional parameters for the better prediction of GISTs clinical behaviour. Tumors with deletion/insertion mutations affecting codons 557/558 of the KIT gene seem to represent a distinct subset of malignant GISTs.
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. GISTs express KIT and show gain-of-function KIT mutations. Most of these mutations affect the KIT juxtamembrane domain, but other KIT domains are mutated at a lower frequency. In this study, frequency of GCC TAT insertion mutation (1530ins6) in KIT exon 9 (extracellular domain) and its possible clinicopathologic significance was investigated. Screening of 520 GISTs identified 26 cases with 1530ins6 KIT mutation and confirmed the previously reported low frequency of this type of KIT mutation among GISTs of different locations. Of the 26 tumors with 1530ins6 KIT mutation studied, 21 originated from the small intestine, 1 from the colon, and 3 from the rectum. In 1 case, primary small intestinal versus colonic localization could not be clearly established because of intra-abdominal dissemination. No distinctive morphological features were identified for the cohort of tumors defined by 1530ins6 KIT mutations. Most of the tumors showed predominant spindle cell morphology, and a few cases had epithelioid or pleomorphic histological features. Following previously published criteria based on tumor size and mitotic rate, 22 of 26 (85%) tumors were classified as malignant or potentially malignant, and 4 (15%) were classified as probably benign. A malignant clinical course was documented in 18 of 19 tumors from the malignant category. The survival times of 11 patients who died of disseminated GISTs ranged from 1 month to 105 months (median survival time, 26 months). In contrast, 2 of 4 GISTs assigned as probably benign tumors with follow-up information had long disease-free survival. GISTs carrying 1530ins6 occur exclusively in the intestinal location, and a great majority of these tumors follow a malignant course.
Familial gastrointestinal stromal tumor (GIST) syndrome is a rare autosomal dominant genetic disorder. We report on a kindred in which 3 family members carry a germline mutation (c.1727T>C, p.L576P) in exon 11 of the KIT gene. This mutation was not reported so far in familial GISTs. Apart from multiple GISTs in 2 of the mutation carriers, all of them had multiple hyperpigmented skin macules and a history of achalasia-like stenosis of the esophagus in early childhood. In the index patient >100 tumors and a diffuse Cajal cell hyperplasia of the small bowel occurred. Sequencing of DNA extracted from tumor tissue of one of his GISTs revealed the KIT mutation in exon 11 (c.1727T>C). By array comparative genomic hybridization whole chromosomal gains 3, 5, 7, 9, 12, 15, and 18 were detected. In addition, we could identify a gain on chromosome 4, spanning the KIT gene. Together with the family described here, 24 unrelated cases with proven germline mutations in KIT have been reported. In these families the diagnosis was established from the age of 30 years onwards. Because in 1 patient reported here the GIST was a coincidental finding at the age of 15 years, the tumors might occur at a very young age and remain unnoticed until they-either due to increasing size, ulceration, or malignant progression-become symptomatic. Therefore, we propose to start screening patients with known KIT mutations from a younger age.
Inflammatory fibroid polyps (IFP) are mesenchymal tumours of the gastrointestinal tract. This study was performed to broaden the base of evidence of the pathogenic role of PDGFR mutations in IFP with particular regard to clinicopathological data and mutational patterns among IFP subtypes.
Molecular analysis of 38 tumours revealed activating mutations in three different exons of PDGFRA in 25 IFP. For the first time we report two cases with PDGFRA-exon 14 mutations (p.N659K; p.[N659K(+)T665A]). The results of our study and cases reported earlier indicate clearly that there is a localization-specific pattern: exon 12 mutations predominate in the small intestine, while exon 18 mutations occur frequently in the stomach (P < 0.001). Codons 567-571 of PDGFRA represent an IFP specific mutational hot spot and are affected most frequently by deletions. Furthermore, in our series IFP of the stomach share common features. In contrast to intestinal IFP, gastric tumours occur at higher age, show heavy inflammation and tend to be smaller. IFP located in the small intestine are frequently associated with intussusception.
We conclude that there is a 'small bowel' and a 'gastric' phenotype of IFPs which are associated with exon 12 and exon 18 PDGFRA mutations, respectively.
Although Gastrointestinal stromal tumors (GISTs) affect about 0.0014% of the population, GISTs smaller than 1 cm (microGISTs) are detectable in about 20% to 30% of elderly individuals. This suggests that microGISTs likely represent premalignant precursors that evolve only in a minute fraction of cases toward overt GISTs. We sought histopathologic and molecular explanations for the infrequent clinical progression in small GISTs. To investigate the mechanisms of GIST progression and identify subsets with differential malignant potential, we carried out a thorough characterization of 170 GISTs <2 cm and compared their KIT/PDGFRA status with overt GISTs. The proliferation was lower in microGISTs compared with GISTs from 1 to 2 cm (milliGISTs). In addition, microGISTs were more frequently incidental, gastric, spindle, showed an infiltrative growth pattern, a lower degree of cellularity, and abundant sclerosis. The progression was limited to 1 ileal and 1 rectal milliGISTs. KIT/PDGFRA mutations were detected in 74% of the cases. The overall frequency of KIT/PDGFRA mutation and, particularly, the frequency of KIT exon 11 mutations was significantly lower in small GISTs compared with overt GISTs. Five novel mutations, 3 in KIT (p.Phe506Leu, p.Ser692Leu, p.Glu695Lys) 2 in PDGFRA (p.Ser847X, p.Ser667Pro), plus 4 double mutations were identified. Small GISTs share with overt GIST KIT/PDGFRA mutation. Nevertheless, microGISTs display an overall lower frequency of mutations, particularly canonical KIT mutations, and also carry rare and novel mutations. These molecular features, together with the peculiar pathologic characteristics, suggest that the proliferation of these lesions is likely sustained by weakly pathogenic molecular events, supporting the epidemiologic evidence that microGISTs are self-limiting lesions.
The aim of this study was to identify the characteristics of PDGFRA-mutated gastrointestinal stromal tumours (GISTs) in comparison with KIT-mutated GISTs.
A total of 151 GISTs were examined for KIT and PDGFRA mutations, and clinical and histopathological parameters were evaluated and analysed statistically according to mutation status.
KIT and PDGFRA mutations were detected in 123 (81.5%) and 15 cases (9.9%), respectively. Clinically, all PDGFRA-mutated GISTs were located in the stomach with no recurrences and tumour-related deaths were noted. Pathological parameters associated with PDGFRA mutations were epithelioid and mixed type, low to moderate cellularity, moderate to severe intratumoural lymphocytic infiltration, prominent myxoid change, frequent rhabdoid cells and multinucleated giant cells, increased cellular pleomorphism, low mitotic count, and lower risk assessment (p < 0.05). Compared with KIT-mutated GISTs, PDGFRA-mutated GISTs had unique histopathological patterns, intermingling of spindle and epithelioid cells, and/or a jigsaw puzzle-like arrangement of epithelioid cells.
PDGFRA-mutated GISTs have distinctive histological patterns that are differentiated from KIT-mutated GISTs. The algorithmic approach by a combination of several distinguishing histological and immunohistochemical features between KIT- and PDGFRA-mutated GISTs might be helpful in predicting the mutated gene of each GIST on pathological examination.
MicroRNAs are known to regulate gene expression. Although unique microRNA expression profiles have been reported in several tumors, little is known about microRNA expression profiles in GISTs. To evaluate the relationship between microRNA expression and clinicopathologic findings of GISTs, we analyzed the microRNA expression profiles of GISTs. We used fresh frozen tissues from 20 GISTs and analyzed KIT and PDGFRA mutations and chromosomal loss status. MicroRNA expression was analyzed using a microRNA chip containing 470 microRNAs. Using unsupervised hierarchical clustering analysis, we found four distinct microRNA expression patterns in our 20 GISTs. Six GISTs that did not have 14q loss formed a separate cluster. In the 14 GISTs with 14q loss, 5 small bowel GISTs formed a separate cluster and the remaining 9 GISTs could be divided into two groups according to frequent chromosomal losses and tumor risk. We found 73 microRNAs that were significantly down-regulated in the GISTs with 14q loss; 38 of these microRNAs are encoded on 14q. We also found many microRNAs that were down-regulated in small bowel and high-risk group GISTs. Most of the microRNAs down-regulated in the high-risk group and small bowel GISTs are known to be involved in tumor progression, specifically by stimulating mitogen-activated protein kinase (MAPK) and the cell cycle. The microRNA expression patterns of GISTs are closely related to the status of 14q loss, anatomic site, and tumor risk. These findings suggest that microRNA expression patterns can differentiate several subsets of GISTs.
Introduction. Gastrointestinal stromal tumors (GISTs) are characterized at the molecular level by c-kit or PDGFRA oncogene mutations. Although GISTs raised major interest in past decades, population-based studies are still rare. Materials and Methods. All GISTs diagnosed in Southern Switzerland (1999-2005) were identified using Ticino Cancer Registry and analysed for c-kit and PDGFRA mutations. Clinical and molecular features were studied. Results. Annual incidence of GISTs was 1.47 cases/100,000 inhabitants (median age: 64 years; median size: 6.0 cm). Most GISTs arose in the stomach (60.5%). The malignancy risk was very-low/low in 47% of patients. DNA sequences showed a gene alteration in either c-kit or PDGFRA genes in 72.5% of patients. Mutations occurred mostly in c-kit exon 11 (60%). No mutations in c-kit exons 13 or 17 were found. An equal number of alterations in exons 12 and 18, and no mutations in exon 14 were observed in the PDGFRA gene. Discussion. This is the first comprehensive population-based study of GISTs incidence and molecular biology characterization in Central Europe. Our incidence data showed higher age-standardized rates compared to other European countries. The gene mutation spectrum differed when compared to the literature. This is relevant to improve the molecular profile knowledge based on Cancer Registry data.
Gastrointestinal stromal tumors (GISTs), the most common mesenchymal tumors of the gastrointestinal tract, typically express the KIT protein. Activating mutations in the juxtamembrane domain (exon 11) of the c-kit gene have been shown in a subset of GISTs. These mutations lead into ligand-independent activation of the tyrosine kinase of c-kit, and have a transforming effect in vitro. Several groups have studied the clinical implication of the c-kit mutation status of exon 11 in GISTs and a possible relationship between c-kit mutations and malignant behavior has been established. Recently, a 1530ins6 mutation in exon 9 and missense mutations, 1945A>G in exon 13 of the c-kit gene were reported. The frequency and clinical importance of these findings are unknown. In this study we evaluated 200 GISTs for the presence of mutations in exons 9 and 13 of c-kit. Six cases revealed 1530ins6 mutation in exon 9 and two cases 1945A>G mutation in exon 13. All tumors with mutations in exon 9 and 13 lacked mutations in exon 11 of c-kit. None of the analyzed tumors had more than one type of c-kit mutation. All but one of the eight tumors with mutations in exon 9 or 13 of the c-kit gene were histologically and clinically malignant. All four of six cases with exon 9 mutation of which location of primary tumor was known, were small intestinal, suggesting that this type of mutation could preferentially occur in small intestinal tumors. Exon 9 and 13 mutations seem to be rare, and they cover only a small portion (8%) of the balance of GISTs that do not have mutations in exon 11 of c-kit. This finding indicates that other genetic alterations may activate c-kit in GISTs, or that KIT is not activated by mutations in all cases.
Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal tumours of the human gastrointestinal tract. Previous studies of GISTs found gain-of-function mutations of the c-kit gene, which encodes a receptor tyrosine kinase (KIT). All the mutations were confined to exon 11, which encodes the juxtamembrane domain. By further examination of the whole coding region of c-kit complementary DNA in 35 GISTs, two were found to show the identical mutation at exon 9, which encodes the extracellular domain. The aims of the present study were to examine the frequency of the extracellular domain mutation and to determine whether the mutation is a gain-of-function type or not. Genomic DNA was extracted from paraffin-embedded tissues of 133 GISTs and exon 9 of the c-kit gene was amplified by polymerase chain reaction. Screening of the mutation was carried out by single-strand conformation polymorphism analysis and direct sequencing was done. Mutant c-kit cDNA was transfected into 293T human embryonic kidney cells and the magnitude of autophosphorylation of the mutant KIT was examined with or without the ligand of KIT, stem cell factor (SCF). In total, seven GIST cases (approximately 5%) were found with the identical mutation at exon 9. The mutant KIT exhibited constitutive autophosphorylation without SCF stimulation. The prognosis of the patients with the extracellular domain mutation was comparable to that of the patients with the juxtamembrane domain mutation.
Gain-of-function mutation in c-kit proto-oncogene exon 11 has been described in about 20 -- 50% of gastrointestinal stroma tumor (GIST). Recently, additional mutational hot-spots in exon 9 and exon 13 of the c-kit gene have been reported in GISTs without mutations of exon 11, but a subsequent report in a Western population indicated that only a small portion of GISTs (eight of 200 GISTs, 4%) showed mutations in these regions. In this study, we evaluated mutations in exon 9 and exon 13 of the c-kit gene by both polymerase chain reaction-single strand conformation polymorphism analysis and direct sequencing in 48 GISTs in a Japanese population, for which the clinicopathological and immunohistochemical features and mutations in exon 11 had previously been reported. C-kit gene mutation in exon 9, representing insertion of GCC TAT, was identified in only 4 of 48 GISTs (8%), and none of the GISTs had mutations in exon 13. All four GISTs with mutation in exon 9 were high-risk, and the patients died of multiple tumor metastasis. Mutations in exon 9 and exon 13 of the c-kit gene were also rare events in Japanese GISTs and were related to a poor prognosis. These results in Japanese are consistent with those in Western populations, although a preferential occurrence of GISTs with exon 9 mutation in the small intestine, which was suggested in a previous report, was not observed.
Activating mutations of the KIT juxtamembrane region are the most common genetic events in gastrointestinal stromal tumors (GISTs) and have been noted as independent prognostic factors. The impact of KIT mutation in other regions, such as the extracellular or kinase domains, is not well-defined and fewer than 30 cases have been published to date.
One hundred twenty GISTs, confirmed by KIT immunoreactivity, were evaluated for the presence of KIT exon 9, 11, 13, and 17 mutations. The relation between the presence/type of KIT mutation and clinicopathological factors was analyzed using Fisher's exact test and log-rank test.
Forty-four % of the tumors were located in the stomach, 47% in the small bowel, 6% in the rectum, and 3% in the retroperitoneum. Overall, KIT mutations were detected in 78% of patients as follows: 67% in exon 11, 11% in exon 9, and none in exon 13 or 17. The types of KIT exon 11 mutations were heterogeneous and clustered in the classic "hot spot" at the 5' end of exon 11. Seven % of cases showed internal tandem duplications (ITD) at the 3' end of exon 11, in a region that we designate as a second hot spot for KIT mutations. Interestingly, these cases were associated with: female predominance, stomach location, occurrence in older patients, and favorable outcome. There were significant associations between exon 9 mutations and large tumor size (P < 0.001) and extragastric location (P = 0.02). Ten of these 13 patients with more than 1-year follow-up have developed recurrent disease.
Most KIT-expressing GISTs show KIT mutations that are preferentially located within the classic hot spot of exon 11. In addition, we found an association between a second hot spot at the 3'end of exon 11, characterized by ITDs, and a subgroup of clinically indolent gastric GISTs in older females. KIT exon 9 mutations seem to define a distinct subset of GISTs, located predominantly in the small bowel and associated with an unfavorable clinical course.
Most gastrointestinal stromal tumors (GISTs) express constitutively activated mutant isoforms of KIT or kinase platelet-derived growth factor receptor alpha (PDGFRA) that are potential therapeutic targets for imatinib mesylate. The relationship between mutations in these kinases and clinical response to imatinib was examined in a group of patients with advanced GIST.
GISTs from 127 patients enrolled onto a phase II clinical study of imatinib were examined for mutations of KIT or PDGFRA. Mutation types were correlated with clinical outcome.
Activating mutations of KIT or PDGFRA were found in 112 (88.2%) and six (4.7%) GISTs, respectively. Most KIT mutations involved exon 9 (n = 23) or exon 11 (n = 85). All KIT mutant isoforms, but only a subset of PDGFRA mutant isoforms, were sensitive to imatinib, in vitro. In patients with GISTs harboring exon 11 KIT mutations, the partial response rate (PR) was 83.5%, whereas patients with tumors containing an exon 9 KIT mutation or no detectable mutation of KIT or PDGFRA had PR rates of 47.8% (P =.0006) and 0.0% (P <.0001), respectively. Patients whose tumors contained exon 11 KIT mutations had a longer event-free and overall survival than those whose tumors expressed either exon 9 KIT mutations or had no detectable kinase mutation.
Activating mutations of KIT or PDGFRA are found in the vast majority of GISTs, and the mutational status of these oncoproteins is predictive of clinical response to imatinib. PDGFRA mutations can explain response and sensitivity to imatinib in some GISTs lacking KIT mutations.
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. GISTs express KIT and show gain-of-function KIT mutations. Most of these mutations affect the KIT juxtamembrane domain, but other KIT domains are mutated at a lower frequency. In this study, frequency of GCC TAT insertion mutation (1530ins6) in KIT exon 9 (extracellular domain) and its possible clinicopathologic significance was investigated. Screening of 520 GISTs identified 26 cases with 1530ins6 KIT mutation and confirmed the previously reported low frequency of this type of KIT mutation among GISTs of different locations. Of the 26 tumors with 1530ins6 KIT mutation studied, 21 originated from the small intestine, 1 from the colon, and 3 from the rectum. In 1 case, primary small intestinal versus colonic localization could not be clearly established because of intra-abdominal dissemination. No distinctive morphological features were identified for the cohort of tumors defined by 1530ins6 KIT mutations. Most of the tumors showed predominant spindle cell morphology, and a few cases had epithelioid or pleomorphic histological features. Following previously published criteria based on tumor size and mitotic rate, 22 of 26 (85%) tumors were classified as malignant or potentially malignant, and 4 (15%) were classified as probably benign. A malignant clinical course was documented in 18 of 19 tumors from the malignant category. The survival times of 11 patients who died of disseminated GISTs ranged from 1 month to 105 months (median survival time, 26 months). In contrast, 2 of 4 GISTs assigned as probably benign tumors with follow-up information had long disease-free survival. GISTs carrying 1530ins6 occur exclusively in the intestinal location, and a great majority of these tumors follow a malignant course.
Gastrointestinal (GI) stromal tumors (GISTs), the specific KIT- or PDFGRA-signaling driven mesenchymal tumors, are the most common mesenchymal tumors of the GI tract. In this study, we analyzed 1869 cases originally classified as smooth muscle tumors of the stomach and found that 1765 (94%) of these were GISTs. The GISTs had a slight male predominance (55%) with a median age of 63 years. Only 2.7% of tumors occurred before the age of 21 years and 9.1% before the age of 40 years. The tumors varied from 0.5 to 44 cm (median, 6.0 cm) and most commonly presented with GI bleeding; 12% were incidentally detected. Several histologic variants were recognized among the spindle cell tumors (sclerosing, palisaded-vacuolated, hypercellular, and sarcomatous) and of epithelioid tumors (sclerosing, dyscohesive, hypercellular, and sarcomatous). Outcome was strongly dependent on tumor size and mitotic activity. Only 2% to 3% of tumors <10 cm and <5 mitoses/50 HPFs metastasized, whereas 86% of tumors >10 cm and >5 mitoses/50 HPFs metastasized. However, tumors >10 cm with mitotic activity <5/50 HPFs and those <5 cm with mitoses >5/50 HPFs had a relatively low metastatic rate (11% and 15%). A small number of patients survived intra-abdominal metastasis up to over 20 years. Tumor location in fundus or gastroesophageal junction, coagulative necrosis, ulceration, and mucosal invasion were unfavorable factors (P <0.001), whereas tumor location in antrum was favorable (P <0.001). KIT expression was detected in 91% of the cases, CD34 in 82%, smooth muscle actin in 18%, and desmin in 5%; the latter two were favorable (P <0.001). KIT exon 11 mutations were detected in 119 cases; patients with point mutations fared better than those with deletions (P <0.01). PDGFRA exon 18 mutations (total 86 cases) were common in epithelioid GISTs and most commonly represented a D842V point mutation; none of these was prognostically significant. The above results may be helpful for setting the criteria for adjuvant treatment such as Gleevec.
To describe the clinical characteristics, molecular features, treatment, and outcome of six pediatric patients with gastrointestinal stromal tumors (GISTs).
Retrospective clinical review of GISTs, seen at The Hospital for Sick Children (HSC) Toronto, over an 11-year period. All specimens were stained for the CD 117 and CD 34 antigens. Three specimens were sequenced for mutations in exons 9, 11, and 13 of the c-kit gene.
Five patients were evaluated and treated at HSC and one was referred for histopathological consultation only. The median patient age at diagnosis was 13.6 years, (6.9-14.8 years); four were female. All patients presented with anemia secondary to gastrointestinal (GI) bleeding. The disease was localized in five patients and two had other malignancies consistent with the diagnoses of Carney's triad. Immunohistochemical staining for CD 117 and CD 34 showed heavy cytoplasmic localization in all of the tumor cells. A novel point mutation of KIT in codon 456 of exon 9 was found in one case. Complete surgical resection was achieved in the five patients managed at our center and none received adjuvant therapies. Disease recurred locally in one patient. Four patients are alive and one is lost to follow-up.
In children and adolescents, GISTs should be considered in the differential diagnosis of anemia secondary to GI hemorrhage. The absence of an exon 11 mutation and the identification of a novel mutation in exon 9 suggest that pediatric GISTs may respond differently to currently available targeted therapies and therefore should be studied within the context of collaborative group trials.
To explore the prognostic value of mutations in c-KIT and PDGFR-alpha genes with respect to relapse-free survival (RFS) in patients with gastrointestinal stromal tumors (GIST). We have investigated the prognostic relevance of the type and position of the mutations, in addition to other clinicopathologic factors, in a large series of patients with GIST.
For this study, 162 patients were selected according to the following criteria: completely resected tumors with negative margins attended between 1994 and 2001; no metastasis at diagnosis; tumor larger than 2 cm, c-KIT-positive immunostaining; and no other primary tumors.
The median follow-up was 42 months for patients free of recurrence. Mutations were detected in 96 tumors (60%): 82 cases involving c-KIT and 14 cases involving PDFGR-alpha. Univariate analysis demonstrated the following as poor prognostic factors for RFS: tumors larger than 10 cm (P < .0001); mitotic count higher than 10 mitoses per 50 high-power fields (P < .0001); high risk index (P < .0001); intestinal GIST location (P = .0041); high cellularity (P < .0001); tumor necrosis (P < .0001); deletions affecting exon 11 (P = .0007); and deletions affecting codons 557 to 558 (P < .0001). After the multivariate analysis, only the high risk index (relative risk [RR], 12.36), high cellularity (RR, 3.97), and deletions affecting codons 557 to 558 of c-KIT (RR, 2.57) corresponded to independent prognostic factors for RFS in GIST patients.
Deletions affecting codons 557 to 558 are relevant for the prognosis of RFS in GIST patients. This critical genetic alteration should be considered to be a new prognostic stratification variable for randomized trials exploring imatinib mesylate in the adjuvant setting in GIST patients.
Gastrointestinal stromal tumors are mesenchymal tumors arising in the stomach and small bowel and more rarely in the rectum, esophagus, peritoneum and retroperitoneum. These tumors are characterized by KIT or PDGFRA mutations. KIT mutations are all in frame and lead to constitutive tyrosine kinase domain activation without ligand binding. Mutations concern four exons (9, 11, 13 and 17) but mainly exon 11. We report a new mutation in exon 9, since only AY 502-503 duplication/insertion, FAF 506 insertion and P456S substitution have been previously reported. This mutation consists of a large deletion of 43 nucleotides and an insertion of 25 nucleotides. More surprisingly, the sequence inserted corresponds to the complementary sequence of the wild allele but in the opposite sense. To our knowledge, this mutation has never been previously described.
Gastrointestinal (GI) stromal tumors (GISTs), the specific KIT- or PDFGRA-signaling driven mesenchymal tumors, are the most common mesenchymal tumors of the GI tract. This study analyzed 1091 tumors originally classified as smooth muscle tumors of the small intestine (including jejunum or ileum and excluding duodenum), and found that 906 (83%) of these were GISTs. The GIST patients had 55:45 male-to-female ratio with a median age of 59 years (range, 13-94 years). Only 0.6% of tumors occurred before the age of 21 years and 13.6% before the age of 40 years. The tumors varied from 0.3 to 40 cm (median, 7.0 cm) and most commonly presented with GI bleeding or acute abdomen; 18% were incidentally detected. Histologically, the tumors were relatively monotypic with spindle cell (86%), epithelioid (5%), or mixed patterns (9%). Skeinoid fibers were present in 44% of cases, and their presence was associated with a favorable course. Most epithelioid tumors were malignant, and this morphology sometimes emerged from less cellular and less mitotically active spindle cell tumors, suggesting that it represented a transformation. KIT was immunohistochemically detected in 98%, CD34 in 40%, smooth muscle actin in 34%, desmin in 0.2%, and S-100 protein in 14% of the tumors tested. Outcome was strongly dependent on tumor size and mitotic activity, with an overall 39% tumor-related mortality, twice that for gastric GISTs. Only <3% of tumors <5 cm and < or = 5 mitoses/50 HPF metastasized, whereas 86% of tumors >10 cm and >5 mitoses/50 HPF metastasized. In stark contrast to corresponding gastric tumors, tumors >10 cm with mitotic activity < or = 5/50 HPF and those < or = 5 cm with mitoses >5/50 HPF had a high metastatic rate (>50%); tumors >5 cm < or = 10 cm with low mitotic rate had a 24% metastatic rate. The median survival times of patients with low mitotic rate tumors who died of disease decreased by increasing tumor size. KIT exon 11 mutations were detected in 90 cases, exon 9 mutation in 17 cases, and exon 17 mutation in 1 case; the presence of mutation or mutation type was not prognostically significant. There were no PDGFRA exon 12 or 8 mutations. Systematic data on prognosis of small intestinal GISTs of various size and mitotic activity categories can be helpful in management and surveillance of patients with these tumors.
A recent randomized EORTC phase III trial, comparing two doses of imatinib in patients with advanced gastrointestinal stromal tumours (GISTs), reported dose dependency for progression-free survival. The current analysis of that study aimed to assess if tumour mutational status correlates with clinical response to imatinib. Pre-treatment samples of GISTs from 377 patients enrolled in phase III study were analyzed for mutations of KIT or PDGFRA by combination of D-HPLC and direct sequencing of tumour genomic DNA. Mutation types were correlated with patients' survival data. The presence of exon 9-activating mutations in KIT was the strongest adverse prognostic factor for response to imatinib, increasing the relative risk of progression by 171% (P<0.0001) and the relative risk of death by 190% (P<0.0001) when compared with KIT exon 11 mutants. Similarly, the relative risk of progression was increased by 108% (P<0.0001) and the relative risk of death by 76% (P=0.028) in patients without detectable KIT or PDGFRA mutations. In patients whose tumours expressed an exon 9 KIT oncoprotein, treatment with the high-dose regimen resulted in a significantly superior progression-free survival (P=0.0013), with a reduction of the relative risk of 61%. We conclude that tumour genotype is of major prognostic significance for progression-free survival and overall survival in patients treated with imatinib for advanced GISTs. Our findings suggest the need for differential treatment of patients with GISTs, with KIT exon 9 mutant patients benefiting the most from the 800 mg daily dose of the drug.
Mutually exclusive KIT and PDGFRA mutations are central events in GIST pathogenesis, and their understanding is becoming increasingly important, because specific treatment targeting oncogenic KIT and PDGFRA activation (especially imatinib mesylate) has become available. KIT mutations in GIST are clustered in four exons. Most common are exon 11 (juxtamembrane domain) mutations that include deletions, point mutations (affecting a few codons), and duplications (mostly in the 3′ region). The latter mutations most often occur in gastric GISTs. Among gastric GISTs, tumors with deletions are more aggressive than those with point mutations; this does not seem to hold true in small intestinal GISTs. Exon 9 mutations (5-10%) usually are 2-codon 502-503 duplications, and these occur predominantly in intestinal versus gastric GISTs. Lesser imatinib sensitivity of these tumors has been noted. Kinase domain mutations are very rare; GISTs with such mutations are variably sensitive to imatinib. PDGFRA mutations usually occur in gastric GISTs, especially in the epithelioid variants; their overall frequency is approximately 30% to 40% of KIT mutation negative GISTs. Most common is exon 18 mutation leading Asp842Val at the protein level. This mutation causes imatinib resistance. Exon 12 and 14 mutations are rare. Most mutations are somatic (in tumor tissue only), but patients with familial GIST syndrome have consitutitonal KIT/PDGFRA mutations; >10 families have been reported worldwide with mutations generally similar to those in sporadic GISTs. GISTs in neurofibromatosis 1 patients, children, and Carney triad seem to lack GIST-specific KIT and PDGFRA mutations and may have a different disease mechanism. Secondary mutations usually occur in KIT kinase domains in patients after imatinib treatment resulting in resistance to this drug. Mutation genotyping is a tool in GIST diagnosis and in assessment of sensitivity to kinase inhibitors.
Gastrointestinal (GI) stromal tumors (GISTs) are the most common mesenchymal tumors specific to the GI tract, generally defined as KIT (CD117)-positive tumors with a characteristic set of histologic features. These tumors, derived from Cajal cells or their precursors, most commonly occur at the age >50 years in the stomach (60%), jejunum and ileum (30%), duodenum (4-5%), rectum (4%), colon and appendix (1-2%), and esophagus (<1%), and rarely as apparent primary extragastrointestinal tumors in the vicinity of stomach or intestines. Their overall incidence has been estimated as 10 to 20 per million, including incidental minimal tumors. GISTs are rare in children (<1%) and almost exclusively occur in stomach. They are common in patients with neurofibromatosis 1, who have a predisposition to (multiple) small intestinal GISTs. GISTs contain a spectrum from minute indolent tumors to sarcomas at all sites of occurrence. Their gross patterns are diverse, including nodular, cystic, and diverticular tumors. External involvement of pancreas and liver can simulate primary tumor in these organs. In general, gastric tumors have a more favorable prognosis than the intestinal ones with similar parameters. Gastric GISTs < or =10 cm and < or =5 mitoses per 50 HPFs have a low risk for metastasis, whereas those with >5 per 50 HPFs and >5 cm in diameter have a high risk for metastasis. In contrast, all intestinal GISTs >5 cm independent of mitotic rate have at least moderate risk for metastases, and all >5 mitoses per 50 HPFs have a high risk for metastases. Intestinal GISTs < or =5 cm with < or =5 mitoses per 50 HPFs have a low risk for metastases. Gastric GISTs can be divided into histologic subgroups including 4 spindle cell and 4 epithelioid variants. Intestinal GISTs are a histologically more homogeneous group and often contain distinctive extracellular collagen globules, skeinoid fibers. Immunohistochemical demonstration of KIT, CD34, or protein kinase theta positivity helps to properly identify these tumors.
Gastrointestinal stromal tumors (GISTs) typically express high levels of the Kit-receptor. The majority of GISTs carry mutations in the c-kit protooncogene clustering in exon 11. The significance of c-kit mutations for the biological behavior of GISTs is still under discussion. We evaluated 55 sporadic GISTs with available follow-up data for c-kit mutations in the juxtamembrane domain and detected mutations in 35 cases (63.6%). We found a mutational hotspot in codons 557 (tryptophan) and 558 (lysine) preferentially in histomorphologically malignant tumors. In the group of GISTs carrying c-kit mutations, 16 of 21 malignant, but only 3 of 8 benign GISTs and 3 of 6 lesions with uncertain malignant potential, carried mutations of Trp-557 and/or Lys-558. We investigated whether mutations in these 2 amino acids had an impact on biological behavior. Trp-557 and/or Lys-558 were mutated in all 15 metastatic GISTs carrying c-kit mutations but only in a minority of nonmetastatic tumors. A combined deletion of Trp-557 and Lys-558 occurred exclusively in 8 metastatic GISTs. We conclude that in addition to histomorphological evaluation determination of mutations in exon 11 may be an additional parameter for predicting the metastatic risk of GISTs and may be important for the decision that patients will need close clinical follow-up or further adjuvant treatment with kit antagonists.
Stem Cell Factor (SCF) initiates its multiple cellular responses by binding to the ectodomain of KIT, resulting in tyrosine kinase activation. We describe the crystal structure of the entire ectodomain of KIT before and after SCF stimulation. The structures show that KIT dimerization is driven by SCF binding whose sole role is to bring two KIT molecules together. Receptor dimerization is followed by conformational changes that enable lateral interactions between membrane proximal Ig-like domains D4 and D5 of two KIT molecules. Experiments with cultured cells show that KIT activation is compromised by point mutations in amino acids critical for D4-D4 interaction. Moreover, a variety of oncogenic mutations are mapped to the D5-D5 interface. Since key hallmarks of KIT structures, ligand-induced receptor dimerization, and the critical residues in the D4-D4 interface, are conserved in other receptors, the mechanism of KIT stimulation unveiled in this report may apply for other receptor activation.
Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. Despite clinicopathological differences, GISTs share oncogenic KIT or platelet-derived growth factor-alpha (PDGFRA) mutations. Imatinib, KIT and PDGFRA inhibitor, has been successfully used in the treatment of metastatic GISTs. There are primary KIT or PDGFRA mutations diagnosed before imatinib treatment, linked to GIST pathogenesis, and secondary mutations detected during treatment, causing drug resistance. KIT exon 11 mutations are the most common. Gastric GISTs with exon 11 deletions are more aggressive than those with substitutions. KIT exon 11 mutants respond well to imatinib. Less common KIT exon 9 Ala502_Tyr503dup mutants occur predominantly in intestinal GISTs and are less sensitive to imatinib. An Asp842Val substitution in exon 18 is the most common PDGFRA mutation. GISTs with such mutation are resistant to imatinib. PDGFRA mutations are associated with gastric GISTs, epithelioid morphology and a less malignant course of disease. GISTs in neurofibromatosis 1, Carney triad and paediatric tumours generally lack KIT and PDGFRA mutations. Secondary KIT mutations affect exons 13-17. GISTs with secondary mutations in exon 13 and 14 are sensitive to sunitinib, another tyrosine kinase inhibitor. KIT and PDGFRA genotyping is important for GIST diagnosis and assessment of sensitivity to tyrosine kinase inhibitors.
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