Luis Requena’s research while affiliated with Autonomous University of Madrid and other places

Accurate melanoma diagnosis is crucial for patient outcomes and reliability of AI diagnostic tools. We assess interrater variability among eight expert pathologists reviewing histopathological images and clinical metadata of 792 melanoma-suspicious lesions prospectively collected at eight German hospitals. Moreover, we provide access to the largest panel-validated dataset featuring dermoscopic and histopathological images with metadata. Complete agreement is achieved in 53.5% of cases (424/792), and a majority vote ( ≥ five pathologists) in 90.9% (720/792). Considerable discordance is observed for non-invasive melanomas (complete agreement in only 10/73 cases). The expert panel disagrees with the local pathologists’ and dermatologists’ diagnoses in 14.9% and 33.5% of cases, respectively. This variability highlights the diagnostic challenges of early-stage melanomas and the need to reconsider how ground truth is established in routine care and AI research. Including at least two pathologists or virtual panels may contribute to more consistent diagnostic results.

Mycosis fungoides (MF) has been widely reported to mimick a considerable number of different dermatoses, including scarring alopecia, bullous dermatoses or cysts, and comedones. In atypical presentations, histopathology is essential for the diagnosis. We present two cases of MF with clinical urticarial lesions and a striking blood involvement that responded to mogamulizumab treatment. Histopathologically, both cases had classic MF features and shared a peculiar immunophenotype, with positivity for CD25 and FOXP3. Differential diagnoses included urticarial lymphomatoid drug reactions and other lymphomas, like T-cell prolymphocytic leukemia, atypical Sézary syndrome, or adult T-cell lymphocytic leukemia. A low suspicion threshold is necessary for the diagnosis of atypical presentations of MF.

The panniculitides represent a group of heterogeneous inflammatory diseases that involve the subcutaneous fat. The specific diagnosis of these disorders requires histopathological study because different panniculitides usually show monotonous clinical appearance, namely subcutaneous erythematous nodules on the lower extremities. Histopathological study of panniculitis is also challenging because of an inadequate clinicopathological correlation and the evolutionary nature of the lesions. Often, biopsy specimens are taken from late‐stage lesions, which results in non‐specific histopathological findings. In addition, large‐scalpel incisional biopsies are required. However, with adequate biopsy samples a histopathological differential diagnosis between a mostly septal and a mostly lobular panniculitis is straightforward and with adequate clinicopathological correlation, a specific diagnosis may be rendered in most cases of panniculitis. Mostly septal panniculitides with vasculitis include superficial thrombophlebitis and cutaneous polyarteritis nodosa (cutaneous arteritis). Septal panniculitides with no vasculitis may appear as the consequence of dermal inflammatory processes extending to the subcutaneous fat, such as necrobiosis lipoidica, scleroderma, subcutaneous granuloma annulare, rheumatoid nodule and necrobiotic xanthogranuloma, whereas in other cases the inflammatory process involves primarily the connective tissue septa of the subcutis with no participation of the overlying dermis. The most frequent septal panniculitis is erythema nodosum. In contrast, the most common lobular panniculitis with vasculitis is erythema induratum of Bazin (nodular vasculitis). Mostly lobular panniculitides without vasculitis comprise a large list of disorders, including sclerosing panniculitis (lipodermatosclerosis), subcutaneous fat necrosis of the newborn, panniculitis associated with connective tissue diseases, pancreatic panniculitis, 1 ‐antitrypsin deficiency‐associated panniculitis, infective panniculitis and factitious panniculitis. In recent years, several cases of both septal and lobular panniculitis have been described as a consequence of the administration of new drugs, including immune checkpoint inhibitors and BRAF inhibitors used as treatment of metastatic melanoma, tyrosine kinase and Bruton tyrosine kinase inhibitors used for treatment of leukemia and other haematological malignancies and tumour necrosis factor inhibitor drugs.

Perineural infiltration refers to a neoplastic cell involvement in, around, and through the nerves. It is considered as one of the neoplastic dissemination pathways. Thus, its identification is crucial to establish the prognosis of some malignant skin neoplasms, such as squamous cell carcinoma, and explains the locally aggressive behavior of cutaneous neoplasms, such as microcystic adnexal carcinoma. We have conducted a review of malignant and benign skin tumors in which perineural infiltration has been described, and we also discuss some histopathological findings that may simulate perineural infiltration.

Background Merkel cell carcinoma (MCC) is an aggressive malignant neuroendocrine tumour. There are two subsets of MCC, one related to Merkel cell polyomavirus (MCPyV) and the other to ultraviolet (UV) radiation. MCPyV-positive and MCPyV-negative MCCs have been considered to be different tumours, since the former type harbours few DNA mutations and is not related to UV radiation, and the latter usually arises in sun-exposed areas and may be found in conjunction with other keratinocytic tumours, mostly squamous cell carcinomas. Two viral oncoproteins, large T antigen (LT, coded by MCPyV_gp3) and small T antigen (sT, coded by MCPyV_gp4), promote different carcinogenic pathways. Objectives We hypothesized that the biological behaviours of MCPyV-positive and MCPyV-negative MCCs are different. We aimed to determine which genes are differentially expressed in MCPyV-positive and MCPyV-negative MCC, to describe the mutational burden and the most frequently mutated genes in the two MCC types, and to identify the clinical and molecular factors that may be related to patient survival. Methods Ninety-two cases with a diagnosis of MCC were identified from the medical databases of the participating centres. To study gene expression, a customized panel of 172 genes was developed. Gene expression profiling was performed with nCounter Technology (NanoString Technologies, Seattle, WA, USA). For mutational studies, a customized panel of 26 genes was designed. Somatic single nucleotide variants (SNVs) were identified following the best practices GATK workflow for somatic mutations. Results The expression of LT enabled the series to be divided into two groups, (LT-positive, n=55; LT-negative, n=37). Genes differentially expressed in LT-negative cases were related to epithelial differentiation, especially SOX9, or proliferation and cell cycle (MYC, CDK6), among others. Congruently, LT displayed lower expression in SOX9-positive cases, and differentially expressed genes in SOX9-positive cases were related to epithelial/squamous differentiation. In LT-positive cases, the mean SNV frequency was 4.3 per case, and 10 per case in LT-negative cases (p=0.03). The expression of SNAI1 (HR=1.046, 95% CI=1.007–1.086, p=0.021) and CDK6 (HR=1.049, 95% CI=1.020–1.080, p=0.001) were identified as risk factors in a multivariate survival analysis. Conclusions Tumours with weak expression of LT tend to co-express genes related to squamous differentiation and cell cycle, and to have a higher mutational burden. These findings are congruent with those of earlier studies.

Myeloid neoplasms and acute leukemias include different entities that have been recently re-classified taking into account molecular and clinicopathological features. The myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) category comprises a heterogeneous group of hybrid neoplastic myeloid diseases characterized by the co-occurrence of clinical and pathological features of both myelodysplastic and myeloproliferative neoplasms. The most frequent entity in this category is chronic myelomonocytic leukemia (CMML) which is, after acute myeloid leukemia (AML), the main myeloid disorder prone to develop cutaneous manifestations. Skin lesions associated with myelodysplastic and myeloproliferative neoplasms include a broad clinical, histopathological and molecular spectrum of lesions, poorly understood and without a clear-cut classification in the current medical literature. The aim of this review is to describe and classify the main clinical, histopathological and molecular patterns of cutaneous lesions in the setting of MDS/MPN in order to improve the diagnostic skills of the dermatologists, hematologists and pathologists who deal with these patients.

Myeloid neoplasms and acute leukemias include different entities that have been recently re-classify taking into account molecular and clinicopathological features. The myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) category comprises a heterogeneous group of hybrid neoplastic myeloid diseases characterized by the co-occurrence of clinical and pathologic features of both myelodysplastic and myeloproliferative neoplasms. The most frequent entity in this category is chronic myelomonocytic leukemia (CMML) which is, after acute myeloid leukemia (AML), the main myeloid disorder prone to develop cutaneous manifestations. Skin lesions associated with myelodysplastic and myeloproliferative neoplasms include a broad clinical, histopathological and molecular spectrum of lesions, poorly understood and without a clear-cut classification in the current medical literature. The aim of this review is to describe and classify the main clinical, histopathological and molecular patterns of cutaneous lesions in the setting of MDS/MPN in order to improve the diagnostic skills of dermatologists, hematologist and pathologist who deal with these patients.

ALK-negative anaplastic large cell lymphoma (ALCL) cases with 6p25.3 rearrangement are characterized by peculiar morphological and immunohistochemical features compare to 6p25.3-negative ALK-negative ALCL cases. A subgroup of 6p25.3-positive ALK-negative ALCL cases show the t(6,7)(p25.3;q32.3) rearrangement. Aims: To analyse the differences between 6p25.3-rearranged cases with and without t(6,7)(p25.3;q32.3). Using RNA-sequencing we studied a series of 17 samples showing 6p25.3-rearrangement, identified by FISH, consisting of seven systemic and eight primary cutaneous cases including two examples of secondary skin involvement by systemic ALCL. RNA-sequencing exclusively detected a translocation involving a gene in the 6p25.3 region (either IRF4 or DUSP22) in 7/14 cases (50%). In six of these seven cases the partner proved to be the LINC-PINT region in chromosome 7, while an EXOC2::DUSP22 rearrangement was found in one case. All cases but one were primary cutaneous ALCLs. They all were CD3 positive and BCL2 negative, while most of them expressed p-STAT3. On the contrary, cases without the t(6,7)(p25.3;q32.3) were mainly systemic (71%, 5/7) against just two pcALCL. In general, they lose CD3 (50% positive) and p-STAT3 (25% positive) expression, being all of them BCL2 positive. Moreover, in 60% of them other gene fusions were found. At the transcriptional level, they were characterized by the overexpression of TCF3 (TCF7L1/E2A), DLL3, CD58 and BCL2 genes. 75%(6/8) of pcALCL with 6p25.3 rearrangement featured the so-called "biphasic morphologic pattern, which was not found in cutaneous involvement from systemic ALCL. 83% (5/6) of the pcALCL cases with the "biphasic morphologic pattern" showed the t(6,7)(p25.3;q32.3) rearrangement. ALK-negative ALCL cases with 6p25.3 rearrangement are a subgroup of tumours that are heterogeneous with respect to the presence or absence of the t(6,7)(p25.3;q32.3) translocation.