In recent years, additional targeted and immunotherapy approaches have been introduced with treatment dependent on the biomarkers human epidermal growth factor receptor 2 (HER2), programmed death-ligand 1 (PD-L1) as determined by combined positive score (CPS), mismatch repair deficiency (dMMR), and high microsatellite instability (MSI-H) for advanced incurable gastric cancer. The gene discussed is ERBB2; the disease is gastric cancer.