Prognostic value of the tumor immune microenvironment, PD-L1 and p16^INK4A in penile squamous cell carcinoma

Penile squamous cell carcinoma (PSCC) is a rare disease with limited systemic therapy strategies in advanced stages. To gain a better understanding about tumor and immune-related factors in PSCC with potential implications for future therapeutic options, we assessed T-lymphocytic tumor immune microenvironment (TIME), human papillomavirus (HPV) status, and p16 expression in a retrospective, multi-institutional cohort of 115 PSCC patients. We constructed a tissue microarray (TMA) containing cores from the tumor front (TF) and tumor center (TC) and performed immunohistochemistry (IHC) using antibodies against p16^INK4A, CD3, CD8, and PD-L1. Cluster analysis based on CD3, CD8, and PD-L1 expression revealed two distinct immunophenotypic subgroups. The non-inflamed cluster with low expression of CD3, CD8, and PD-L1, and the inflamed cluster with high expression of these markers. Specific clustering configurations involving IHC assessments from TC highlighted a significantly shorter overall survival and cancer-specific survival for the inflamed cluster compared to the non-inflamed cluster. PD-L1 tumor proportion score (TPS) was higher in cases with vascular and lymphatic invasion, whereas combined positive score (CPS) was higher in samples with lymphatic invasion and lymph node metastasis. p16^INK4A negative cases showed higher PD-L1 TPS/CPS and reduced metastasis free survival compared to p16^INK4A positive samples. Taken together, this study demonstrates the prognostic value of the TIME using the three widely available markers CD3, CD8, and PD-L1 in PSCC. Furthermore, it provides additional evidence for a survival benefit of p16^INK4A positive cases, compared to p16^INK4A negative cases.