Clinicopathological features of 22C3 PD-L1 expression with mismatch repair, Epstein-Barr virus status, and cancer genome alterations in metastatic gastric cancer

BackgroundRecently, the U.S. Food and Drug Administration approved pembrolizumab for patients (pts) with PD-L1-positive metastatic gastric cancer (MGC) based on 22C3 immunohistochemistry (IHC) assay. However, little is known about detailed clinicopathological features of 22C3 PD-L1 expression in MGC.Patients and methodsPts with histologically confirmed MGC were eligible for this prospective observational study. PD-L1 expression (22C3) on tumor cell (TC) or immune cell (IC) and mismatch repair (MMR) were analyzed by IHC. Epstein-Barr virus (EBV) was detected by in situ hybridization. The expressions of tyrosine kinase receptors (RTKs) and cancer genome alterations were evaluated by IHC or next-generation sequencing.ResultsA total of 225 pts were analyzed in this study. PD-L1 expression on TC, PD-L1 on IC, MMR-deficient (D-MMR), and EBV positivity were identified in 8.4, 65.3, 6.2, and 6.2% cases, respectively. PD-L1 expression in TC was more frequently observed in pts with D-MMR (P<0.001), PIK3CA mutation (P=0.020), and KRAS mutation (P=0.002), and PD-L1 on IC was associated with EBV positivity (P=0.034), and lymph-node metastasis (P<0.001). PD-L1 expression on either IC or TC was less frequently observed in pts with peritoneal metastasis and Borrmann Type 4. A significant association was not observed between PD-L1 expression and RTKs expression or presence of other gene alterations. PD-L1 expression on either TC or IC was not prognostic factor.Conclusions22C3 PD-L1 expression in MGC was associated with distinct clinicopathological features, but was not a prognostic factor.