A Robust Immunohistochemical Assay for Detecting PTEN Expression in Human Tumors

Myriad Genetics Inc., Wakara Way, Chipeta Way, Salt Lake City, UT 84109, USA.
Applied immunohistochemistry & molecular morphology: AIMM / official publication of the Society for Applied Immunohistochemistry (Impact Factor: 1.63). 10/2010; 19(2):173-83. DOI: 10.1097/PAI.0b013e3181f1da13
Source: PubMed

ABSTRACT Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a negative regulator of the phosphoinositol-3-kinase (PI3K)/AKT signaling pathway that controls cell cycle progression, growth and inhibition of apoptosis. Loss of PTEN protein expression has been associated with tumorigenesis, cancer progression and drug resistance, but conflicting results exist which may be due in part to difficulties inherent in PTEN immunohistochemistry (IHC). We sought a robust PTEN IHC assay. Human tumor cell lines with PTEN status verified by copy number analysis were formalin fixed and paraffin embedded for use as positive and negative controls. PTEN antibodies were optimized on tumor cell lines. Five optimized antibodies were analyzed on 10 molecularly characterized endometrial carcinoma samples. Four antibodies (CST, Millipore, Abcam, Novus) stained 3/10 positive and 7/10 negative, however, all but CST exhibited nonspecific nucleolar staining of negative controls. One antibody (Dako) stained 5/10 positive and 5/10 negative but with areas (≤10%) of positivity. The 4 samples predicted to be negative by sequencing were negative with the CST antibody, however, one was positive with Dako; as a result we chose the CST antibody for our assay. The assay was validated on an automated platform using 50 formalin fixed and paraffin embedded colon, lung, prostate and breast adenocarcinoma cases. Tumor cell lines served as external controls; endothelial cells and peripheral nerves served as internal positive controls. Dichotomous scoring achieved 100% concordance between three independent pathologists. This reproducible PTEN assay (PREZEON) has been implemented in a CLIA certified laboratory.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ewing Sarcoma is an aggressive malignancy of bone and soft tissue affecting children and young adults. Ewing Sarcoma is driven by EWS/Ets fusion oncoproteins, which cause widespread alterations in gene expression in the cell. Dysregulation of receptor tyrosine kinase signaling, particularly involving IGF-1R, also plays an important role in Ewing Sarcoma pathogenesis. However, the basis of this dysregulation, including the relative contribution of EWS/Ets-dependent and independent mechanisms, is not well understood. In the present study, we identify variable expression of two modifiers of PI3K signaling activity, PIK3R3 and PTEN, in Ewing Sarcoma, and examine the consequences of this on PI3K pathway regulation and oncogenic phenotypes. Our findings indicate that PIK3R3 plays a growth-promotional role in Ewing Sarcoma, but suggest that this role is not strictly dependent on regulation of PI3K pathway activity. We further show that expression of PTEN, a well-established, potent tumor suppressor, is lost in a subset of Ewing Sarcomas, and that this loss strongly correlates with high baseline PI3K pathway activity in cell lines. In support of functional importance of PTEN loss in Ewing Sarcoma, we show that re-introduction of PTEN into two different PTEN-negative Ewing Sarcoma cell lines results in downregulation of PI3K pathway activity, and sensitization to the IGF-1R small molecule inhibitor OSI-906. Our findings also suggest that PTEN levels may contribute to sensitivity of Ewing Sarcoma cells to the microtubule inhibitor vincristine, a relevant chemotherapeutic agent in this cancer. Our studies thus identify PIK3R3 and PTEN as modifiers of oncogenic phenotypes in Ewing Sarcoma, with potential clinical implications.
    PLoS ONE 01/2015; 10(1):e0116895. DOI:10.1371/journal.pone.0116895 · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Objectives To determine whether PTEN status in prostate biopsy represents a predictor of intermediate and long-term oncological outcomes after radical prostatectomy, and whether PTEN status predicts response to androgen deprivation therapy.Methods In a retrospective analysis of 77 men treated by radical prostatectomy who underwent diagnostic biopsy between 1992–2006, biopsy samples were stained for PTEN expression by the PREZEON assay with >10% staining reported as positive. Cox proportional hazards and log–rank models were used to assess the correlation between PTEN loss and clinical outcomes.ResultsDuring a median follow-up period after radical prostatectomy of 8.8 years, 39 men (51%) developed biochemical recurrence, four (5%) had castration-resistant prostate cancer, two (3%) had metastasis and two (3%) died from prostate cancer. PTEN loss was not significantly associated with biochemical recurrence (hazard ratio 2.1, 95% confidence interval 0.9–5.1, P = 0.10), but significantly predicted increased risk of castration-resistant prostate cancer, metastasis and prostate cancer-specific mortality (all log–rank, P < 0.0001), and time from androgen deprivation therapy to castration-resistant prostate cancer (log–rank, P = 0.003). No patient without PTEN loss developed metastases or died from prostate cancer.ConclusionsPTEN loss at the time of biopsy seems to predict time to development of metastasis, prostate cancer-specific mortality and, for the first time, castration-resistant prostate cancer and response to androgen deprivation therapy after radical prostatectomy. If confirmed by larger studies, this would support the use of PTEN loss as an early marker of aggressive prostate cancer.
    International Journal of Urology 09/2014; DOI:10.1111/iju.12571 · 1.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Context.-The PI3K-AKT-mTOR (phosphatidylinositol 3-kinase-AKT-mammalian target of rapamycin) pathway plays a crucial role in a subset of advanced pancreatic neuroendocrine tumors (PanNETs). In breast and endometrial carcinoma, activation of this pathway inhibits progesterone receptor (PR) expression. Objective.-To determine whether combined low expression of PR and phosphatase and tensin homologue (PTEN), a negative regulator of the PI3K-AKT-mTOR pathway, is a prognostic factor. Design.-A total of 160 resected PanNETs (89 low grade and 71 intermediate grade) were analyzed for PR and PTEN immunohistochemical positivity and staining was correlated with metastasis-free survival (MFS) and overall survival (OS). Progesterone receptor staining was scored as positive by using 1% or greater as cutoff. Weak/faint staining in greater than 90% of tumor cells was considered low PTEN positivity. Results.-Most PanNETs (110 cases, 69%) were both PR and PTEN positive, 45 (28%) were either PR or PTEN positive, and only 5 (3%) had a PR-negative and PTEN-low profile. Combined PR-PTEN positivity was significantly associated with MFS in patients with stage I and II disease (P <.001) and OS in all patients (P < .001) and remained a significant predictor of survival after adjusting for other factors. Patients with PR-negative-PTEN-low PanNETs had the shortest median MFS and OS, compared to those with tumors that were either PR or PTEN positive and with tumors positive for both PR and PTEN (P ≤ .001). Conclusion.-Combined immunohistochemical assessment of PR and PTEN may help identify a small subset of PanNETs with more aggressive behavior and may aid in risk stratification.
    Archives of pathology & laboratory medicine 08/2014; 138(8):1027-36. DOI:10.5858/arpa.2013-0195-OA · 2.88 Impact Factor