Frequent Programmed Death-Ligand 1 Expression In Gastric Cancer Associated With Epstein-Barr Virus Or Microsatellite Instability: Implications For Predictive Biomarker Development.

e15579Background: Immune checkpoint blockade of the programmed death-ligand 1 (PD-L1) pathway has emerged as a novel therapeutic approach for cancer. Therefore development of predictive biomarkers, such as PD-L1 expression by immunohistochemistry, may help stratifying patients. However, while PD-L1 expression can be seen in a subset of gastric cancers, it is unclear if it correlates with molecular subtypes, which may be potential confounding factors for patient stratification. Methods: Forty-four resected gastric cancer cases were collected and classified as Epstein-Barr virus positive (EBV+, N = 7), microsatellite unstable (MSI, N = 16), or microsatellite stable tumors without EBV (EBV-/MSS, N = 21). Positive PD-L1 expression was defined as membranous staining in either tumor cells or tumor immune infiltrates. T-cells in immune infiltrates at the tumor invasive front were characterized. Results: Positive PD-L1 expression was seen in 32 (72%) cases. Compared with EBV-/MSS tumors, significantly higher prop...