Among these agents, anti-HER2 therapeutic antibodies (e.g., trastuzumab and pertuzumab), antibody-drug conjugates (ADCs, e.g., trastuzumab emtansine; TDM1), and trastuzumab imaging agents (when radio- or fluorescently-labeled5–8) have changed the prognosis of both breast and gastric cancer patients. The gene discussed is ERBB2; the disease is gastric cancer.