Based on the positive results of the KEYNOTE-059 trial, the anti-PD-1 monoclonal antibody pembrolizumab (Keytruda®, Merck & Co., Inc.)has been approved by the Food and Drug Administration (FDA) for the treatment of patients with programmed cell death-ligand 1 (PD-L1)-positive (> 1%) advanced GC or GEJ adenocarcinoma [78, 79]. This evidence concerns the gene PDCD1 and gastric cancer.