Although the evolution of trastuzumab with the generation of pertuzumab, and the antibody–drug conjugates trastuzumab deruxtecan (T-DXd) and trastuzumab emtansine (T-DM1), has led to improved survival rates for patients with HER2 + breast cancer [7], a substantial number of patients still develop treatment resistance [7, 65]. The gene discussed is ERBB2; the disease is breast cancer.