p53 Immunohistochemistry Defines a Subset of Human Papillomavirus-Independent Penile Squamous Cell Carcinomas with Adverse Prognosis

Background: Penile squamous cell carcinoma (PSCC) is classified into two prognostically distinct types: human papillomavirus (HPV)-associated and HPV-independent. Conversely, the impact of p53 status on prognosis remains controversial. We correlated HPV and p53 status with prognosis in a large series of PSCC patients. p53 was analysed according to a recently described immunohistochemical (IHC) pattern-based framework that includes two normal (scattered, mid-epithelial) and four abnormal patterns (diffuse, basal overexpression, cytoplasmic and null) and closely correlates with TP53 mutational status. Methods: A total of 122 patients with surgically treated PSCC in three hospitals in Barcelona, Spain, were included. Based on HPV in situ hybridization and p16 and p53 IHC expression, the tumors were classified into three molecular types: HPV-associated, HPV-independent/p53 normal, and HPV-independent/p53 abnormal. All patients were followed for at least 22 months (median 56.9 months), and disease-specific survival (DSS) was analysed. Results: Thirty-six tumors (29%) were HPV-associated, 35 (29%) were HPV-independent/p53 normal, and 51 (42%) were HPV-independent/p53 abnormal. Disease-related deaths were observed in 3/36 (8%), 0/35 (0%) and 14/51 (27%) of the patients, respectively (p<0.001). A total of 7/14 deaths in the latter group were patients with tumors showing p53 patterns not recognized in the classical p53 IHC interpretation (basal, null, cytoplasmic). According to our multivariate analysis, HPV-independent/p53 abnormal tumors and advanced stage were associated with impaired DSS (hazard ratio=23.4, 95% confidence interval [CI]= 2.7-3095.3; p=0.001 and 16.3, 95% CI=1.8-2151.5; p=0.008, respectively). CONCLUSION: Compared with patients with HPV-associated and HPV-independent/p53-normal PSCC, patients with HPV-independent/p53 abnormal PSCC have worse clinical outcomes. p53 IHC results define two prognostic categories in HPV-independent PSCC: HPV-independent/p53-normal tumors as low-risk tumors, whereas HPV-independent/p53-abnormal tumors as aggressive neoplasms.