Clinical trials of immune checkpoint blockade (ICB), antibodies, such as anti-programmed cell death protein 1 (PD-1) and anti-programmed death-ligand 1 (PD-L1), showed manageable toxicity and antitumor activity in patients with advanced gastric cancer (GC) in the ATTRACTION-2 and KEYNOTE-059 trials.1 2 However, different studies with ICB treatment revealed a highly variable objective response rate, ranging from 10% to 26% in patients with GC.1 3 4 Hence, the precise biomarkers to discriminate potential responders to immune therapies remains an urgent priority. The gene discussed is PDCD1; the disease is gastric cancer.