PD-L1 Expression in HPV-associated Versus HPV-independent Invasive Vulvar Squamous Cell Carcinoma

Two etiological pathways have been implicated in the pathogenesis of vulvar squamous cell carcinoma (VSCC): a high-risk human papillomavirus (HPV)-associated route and an HPV-independent pathway characterized by TP53 mutations. Programmed cell death ligand 1 (PD-L1) has become increasingly useful in predicting the response to checkpoint inhibitor therapy in squamous cell carcinomas at various anatomical sites. This study aimed to assess the association between PD-L1 expression and the VSCC subtype to evaluate the utility of PD-L1 in prognostication and therapeutic selection based on HPV status. PD-L1 status was assessed using 3 separate metrics for the extent of PD-L1 staining in various cell types: immune cell score, tumor proportion score (TPS), and combined positive score. The study group consisted of 25 HPV-associated and 28 HPV-independent VSCCs. PD-L1 expression was positive in the majority of VSCCs according to all 3 scoring metrics (84.9% by immune cell score, 77.3% by TPS, and 90.6% by combined positive score). PD-L1 expression was observed in the majority of cases in both groups (60%-96.4%). PD-L1 expression using the TPS method was greater in HPV-independent tumors than in HPV-associated tumors ( P = 0.004), and high PD-L1 expression was also more common in the HPV-independent subtype ( P = 0.016 using the TPS method and P = 0.013 using the combined positive score method). Our findings contribute to the growing evidence that PD-L1 is expressed in the majority of invasive VSCCs, and thus may serve as an attractive therapeutic target. PD-L1 expression is higher in HPV-independent tumors, suggesting that this subtype may be more responsive to PD-L1 inhibitor therapy.