Pembrolizumab, an anti programed cell death protein 1 (PD‐1) inhibitor, is currently approved by the US Food and Drug Administration (FDA) for patients with metastatic gastric or GEJ adenocarcinoma whose tumors express programmed death‐ligand 1 (PD‐L1), defined as Combined Positive Score [CPS] ≥1, with disease progression on or after two or more prior lines of therapy.23 This evidence concerns the gene CD274 and gastroesophageal junction adenocarcinoma.