Programmed death ligand-1 and Programmed cell death protein-1 expression across the anal disease continuum and association with improved survival in anal cancer

High-risk human papillomavirus is associated with anal high-grade intraepithelial lesion (aHSIL) and anal squamous cell carcinoma (aSCC). The prognostic significance of PD-L1 expression in aSCC and its impact on overall survival (OS) is controversial. ASCC can evade immune surveillance by co-opting the PD-L1/PD-1 immune checkpoint pathway, enhancing tumorigenesis. To assess the potential role of the PD-L1/PD-1 axis on tumor progression, we assessed PD-L1 and PD-1 expression on epithelial cells (ECs) and immune cells (ICs) by immunohistochemistry in benign anal tissue (n=22), aHSIL (n=22), and aSCC (n=52) from HIV-negative participants and people living with HIV. PD-L1 expression on EC was restricted to tumor cells with no expression in benign and HSIL tissues. PD-1 expression on ICs increased along the disease continuum from benign to SCC. The combined PD-L1 expression score on ECs and ICs showed a substantial increase from benign to aHSIL to aSCC. The combined positive score (CPS) for aSCC was 8.2. PD-L1 expression on IC in aSCC was more prominent than in tumor cells which correlated with increased IC infiltration and interferon-gamma secretion. 92% of aSCC demonstrated an adaptive PD-L1 expression pattern. HIV status did not affect PD-L1/PD-1 expression in benign, aHSIL or aSCC. PD-L1 expression in treatment naive aSCC was associated with improved OS. Those with CPS of 0 had a higher risk of death [Hazard ratio 15.2 (95% CI: 3.3-69, p=0.0004; log-rank p<0.0001)] compared to those with CPS > 0. CPS may indicate the presence of immune activation and serve as a potential prognostic marker. SignificancePD-L1 expression becomes more prominent as HPV-infected anal epithelial tissues progress from pre-cancer to cancer. ASCCs with high PD-L1/PD-1 expression indicates a reactive tumor microenvironment, making them promising candidates for immunotherapy.