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Background & Objective: Penile squamous cell carcinoma (SCC) is an extremely rare malignancy. It is usually caused by chronic human papillomavirus (HPV) 16 and HPV 18 infections. This study was conducted to investigate the immunohistochemical overexpression of p16, a surrogate marker for HPV, and to evaluate its usefulness as a potential diagnostic biomarker. Methods: In this cross-sectional prospective and retrospective cohort study, 56 penile squamous cell carcinoma (SCC) specimens and five penile premalignant specimens were evaluated in Kasturba Medical College, Mangalore, India, from January 2013-December 2018 in terms of clinical and histopathological features. Immunohistochemical expression for p16 in cases and controls was evaluated. Statistical comparison of p16 expression among clinical features, histological subtype, grade, and stages of tumor were done. Results: Analysis of the pattern of p16 staining showed diffuse and strong nuclear and cytoplasmic expression in 32.8% of the cases. There was a highly significant association (P<0.001) of pattern of p16 expression among the HPV and non-HPV subtypes of penile carcinoma. p16 expression was not significantly associated with other prognostic parameters like site of the lesion, lymphovascular invasion, perineural invasion, histologic grade, and pathologic stage. Conclusion: Expression of p16 would be a useful tool in differentiation between the HPV-associated and non-HPV-associated subtypes of penile SCC that may be helpful in prediction of aggressiveness and invasive potential of the respective histologic subtypes. [ABSTRACT FROM AUTHOR]

BackgroundPenile cancer (PC) is an extremely rare malignancy, and the patients at advanced stages have currently limited treatment options with disappointing results. Immune checkpoint inhibitors anti-programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) are currently changing the treatment of several tumors. Furthermore, the microsatellite instability (MSI) and the deficient mismatch repair system (dMMR) proteins represent predictive biomarkers for response to immune checkpoint therapy. Until present, few data have been reported related to PD-L1 expression and MSI in PC. The main aim of our study was the evaluation of PD-L1 expression in tumor cells (TCs) and tumor-infiltrating lymphocytes (TILs) in immune cells and the analysis of dMMR/MSI status in a large series of PCs.MethodsA series of 72 PC, including 65 usual squamous cell carcinoma (USCC), 1 verrucous, 4 basaloid, 1 warty, and 1 mixed (warty-basaloid), was collected. Immunohistochemistry (IHC) was performed to assess PD-L1 expression using two different anti-PD-L1 antibodies (clone SP263 and SP142 Ventana) and MMR proteins expression using anti-MLH1, anti-PMS2, anti-MSH2, and anti-MSH6 antibodies. PCR analysis was performed for the detection of MSI status.ResultsOf the 72 PC cases analyzed by IHC, 45 (62.5%) cases were TC positive and 57 (79%) cases were combined positive score (CPS) using PDL1 SP263. In our cohort, TILs were present in 62 out of 72 cases (86.1%), 47 (75.8%) out of 62 cases showed positivity to PDL1 clone SP142. In our series, 59 cases (82%) had pMMR, 12 cases (16.7%) had lo-paMMR, and only 1 case (1.3%) had MMR. PCR results showed that only one case lo-paMMR was MSI-H, and the case dMMR by IHC not confirmed MSI status.ConclusionOur findings showed that PD-L1 expression and MSI status represent frequent biological events in this tumor suggesting a rationale for a new frontier in the treatment of patients with PC based on the immune checkpoint inhibitors.