PD-L1 expression and survival in p16-negative and -positive squamous cell carcinomas of the vulva.

Aim: Programmed death-ligand 1 (PD-L1) has become a widely used predictive biomarker for therapy with checkpoint inhibitors in a variety of cancers. Here, we studied the expression of PD-L1 in squamous cell carcinomas of the vulva (SCCV) with regard to HPV status via its surrogate marker p16. Additionally, the status of PD-L1 and p16 were analyzed for prognostic information and potential correlation to tumor-infiltrating lymphocytes (TILs).
Methods: PD-L1 was analyzed in 128 cases of SCCV using the tumor proportion score (TPS), the immune cell score (ICS) and the combined positive score (CPS). Cases were immunostained for p16 and analyzed for stromal TILs. PD-L1, p16, and TILs were compared to clinico-pathological parameters and patient's survival.
Results: TPS ≥ 50% and CPS ≥ 50 were correlated to a worse grading (p = 0.028 and p = 0.031), but not to FIGO-stage. CPS ≥ 50 was associated to a worse prognosis with overall survival (p = 0.021) but was not correlated to the progression-free survival. P16-positivity was correlated to a longer progression-free survival (p = 0.006) and overall survival (p = 0.023). PD-L1 expression was independent from p16 status. TILs ≥ 50% were present in 24% of the cases and were strongly correlated to PD-L1 (TPS p = 0.02, ICS p < 0.001, CPS p = 0.001).
Conclusion: Our data demonstrate that PD-L1 expression is frequent in SCCV and independent from p16 status. High PD-L1 expression was associated with an unfavorable outcome whereas p16-positivity turned out to be an independent positive prognostic factor.