Programmed death-ligand 1 expression in gastric adenocarcinoma is a poor prognostic factor in a high CD8+ tumor infiltrating lymphocytes group.

Gastric adenocarcinoma is one of the most common causes of cancer-related death. In this study, we conducted immunohistochemical studies for PD-L1, PD-1, CTLA-4, and CD8 using tissue microarrays from 464 gastric cancer samples and evaluated the correlations between their expression, clinicopathologic factors, and five-year overall survival. PD-L1 and PD-1 expression was significantly correlated with several adverse prognostic pathologic factors, including higher T-stage, diffuse Lauren histologic type, and lymphatic invasion. Conversely, CTLA-4 expression was correlated with factors of favorable clinical outcomes. A complete case analysis revealed that high PD-L1 and PD-1 expression had an adverse effect on five-year overall survival in univariate analyses. Subgroup analyses wherein patients were divided into two groups according to CD8+ tumor infiltrating lymphocyte levels (high and low) showed that high PD-L1 expression was a significant adverse prognostic factor only in the high CD8+ tumor-infiltrating lymphocytes group. Further research and clinical trials are needed to determine the clinical usefulness of these findings.