PD-L1 expression is associated with massive lymphocyte infiltration and histology in gastric cancer

The mechanism of carcinogenesis of gastric cancer (GC) is still unclear now. This study aimed to explore the correlations among PD-L1, Epstein–Barr virus (EBV) infection, lymphocyte infiltration, HER-2 expression, HER-2 gene status, histology and other clinicopathological factors in GC. A total of 44 GC patients with massive lymphocyte infiltration (GC-MLI) and 93 GC patients without massive lymphocyte infiltration were involved in this study. Immunohistochemical analysis was used to test the expression levels of PD-L1 and HER-2. Fluorescence in-situ hybridization (FISH) was used on HER-2-positive cases with a score of 2 + to test the HER-2 gene status. EBV-encoded RNA (EBER) was used to test for EBV infection. In univariate analysis, PD-L1 expression was significantly associated with GC-MLI (p < 0.001), lower age (p = 0.019), EBV infection (p < 0.001), lower HER-2 expression (p = 0.011) and diffuse/mixed type of histology (p = 0.022). EBER-positive cases were significantly associated with GC-MLI (p < 0.001), lower age (p = 0.016), diffuse/mixed type of histology (p = 0.011), and lower HER-2 expression (p = 0.032). In the multivariable logistic regression model, GC-MLI and the diffuse/mixed type histology were identified as two independent factors that affected PD-L1 expression (p < 0.001). Furthermore, PD-L1 positive cases have worse Overall Survival (OS) than do PD-L1 negative cases (p = 0.011). These results suggest that massive lymphocyte infiltration and the diffuse/mixed type histology of GC should be taken into consideration to select the appropriate patients for PD-L1 inhibitory treatment in the future.