p16INK4a expression and survival outcomes in patients with penile squamous cell carcinoma: The M.D. Anderson Cancer Center Experience.

Abstract

5 Background: Penile Squamous Cell Carcinoma (PSCC) is associated with high risk human papillomavirus (HR-HPV) in about 50% of cases. The immunohistochemical test for p16INK4a (p16) is highly correlated with HR-HPV expression and used as prognostic marker for squamous cell carcinomas in various sites. The prognostic role of this marker in PSCC remains unclear. We studied whether the expression of HPV or p16INK4a is associated with survival in a large PSCC cohort. Methods: We conducted a single institution analysis of PSCC patients who received treatment between 1991-2017.Patients with a confirmed diagnosis of PSCC and available tissue were tested for HR-HPV status using the Cobas PCR assay. Histological subtype, tumor grade, LVI and p16 staining patterns were confirmed by an experienced pathologist. Patient characteristics were summarized using descriptive statistics of clinico-pathologic variables. Kaplan-Meier was used to estimate median overall survival (OS) and cancer specific survival (CSS). Log rank test, univariate and multivariate Cox models were applied to identify the prognostic factors for survival. Results: We identified 147 patients with PSCC, with available tissue for testing. The median follow-up was 5.2 years (95% CI; 4.48, 6.68y). Patients with p16(+) tumors showed a significantly longer median OS and CSS in comparison to the p16(–) group (p=0.038 and p=0.012), with respective 5 year OS probability of 73% (95% CI; 0.74, 0.98) in comparison to 56% (95% CI; 0.46, 0.67) and 5 year CSS probability of 89% (95% CI; 0.7, 1) in comparison to 64% (95% CI; 0.54, 0.75). In contrast, HPV status by PCR did not predict survival outcomes, with 5 year CSS probability for HPV(+) of 75% (95% CI; 0.61, 0.91) compared to 65% (95% CI; 0.55, 0.78) for HPV(–) patients. Multivariable analysis to evaluate the association with CSS, showed that p16(+) along with lymph node status was associated with lower risk of death (HR=0.28, 95%CI; 0.09-0.8, p=0.002), and OS (HR=0.49, 95%CI; 0.19-1.24, p=0.13) after adjusting for the covariates. Conclusions: Tumor p16 status was an independent prognostic factor for CSS in our PSCC cohort providing unique information above that of lymph node status alone.