PDCD1 and cancer: Immune therapy targeting programmed cell death 1 (PD-1) and its ligand programmed death ligand 1 (PD-L1) demonstrated favourable therapeutic effects in gastric cancer (GC) in several clinical trials.1,2 PD-L1 expression has been considered a potential biomarker for treatment efficacy in several types of cancer, including melanoma and non-small-cell lung carcinoma (NSCLC).3 However, whether PD-L1 expression is a predictive biomarker for PD-1/PD-L1 inhibitor efficacy in GC remains controversial.1,4