PDCD1 and gastric cancer: In clinical trials ATTRACTION-4 and CheckMate 649, the combination of nivolumab, an anti-PD-1 monoclonal antibody, with chemotherapy has showed significantly longer progression-free survival (PFS), a higher disease control rate (DCR), and a higher objective response rate (ORR), thus leading to its approval as a first-line treatment for advanced gastric cancer [6, 9].