HER2 overexpression and HER2/neu (ERBB2) amplification were the first molecular biomarkers identified to predict the efficacy of targeted therapies in GC, and microsatellite instability-high (MSI-H) and programmed death-ligand 1 positivity (PD-L1+) are established GC biomarkers. The gene discussed is CD274; the disease is gastric cancer.