Programmed Death Ligand 1 (PD-L1) Expression in Epithelial Ovarian Cancer: A Comparison of Type I and Type II Tumors.

Objective: To examine the expression of programmed death ligand 1 (PD-L1) in type I and type II epithelial ovarian cancers (EOC) and its associations with outcomes. Methods: Records of 132 women with EOC were reviewed. Immunostaining of PD-L1 was performed with formalin-fixed, paraffin-embedded specimens. Expression of PD-L1 was classified into four categories (0; 1+; 2+; 3+) according to intensity of expression. Expression of PD-L1 ≥2+ was deemed to be high. Results: Of the 132 women, 75 (56.8%) and 57 (43.2%) women had type I and type II tumors, respectively. Approximately 70% of cases exhibited high PD-L1 expression. There was no significant difference in the rate of high PD-L1 expression between the two EOC types (65.3% versus 59.6%). In type I tumors, high PD-L1 expression was associated with more advanced stages (51.0% versus 34.6%), greater recurrence (46.9% versus 26.9%), and shorter median progression-free survival (27 months versus 62 months) than low expression. In type II tumors, there were no apparent differences between high and low expression of PD-L1 in terms of the percentage of advanced-stage tumors (82.6% versus 79.4%), recurrence (56.5% versus 58.8%), and median progression-free survival (21 months versus 24 months). Conclusion: high PD-L1 expression is associated with worse oncological outcomes in type I EOC. This finding emphasizes the merit of further studies to confirm this promising result and to determine the potential role of PD-L1 blockade therapy in type I EOC.