It is noteworthy that the mutation frequency of ARID1A significantly varies within different molecular subtypes of gastric cancer: for microsatellite instability (MSI) type, Epstein–Barr virus (EBV) infection type, and non-EBV-infected and microsatellite stable (MSS) type, the mutation rate is 83%, 73%, and 11%, respectively (49), among which MSI and EBV types have higher PD-L1 expression, indicating ARID1A may be a potential biomarker for PD-1/PD-L1 inhibition. This evidence concerns the gene ARID1A and gastric cancer.