The PD-1 inhibitors pembrolizumab and nivolumab, in combination with fluoropyrimidine- and platinum-containing chemotherapy (CT), have received broad regulatory approval for the 1L treatment of adults with unresectable, advanced or metastatic human epidermal growth factor receptor 2 (HER2)-negative GC/GEJC, including in the United States (US) and European Union (EU), and are recommended as treatment options in clinical practice guidelines for patients whose tumors express programmed cell death-ligand 1 (PD-L1) [16–21]. The gene discussed is PDCD1; the disease is gastric cancer.