Following trastuzumab, three HER2‐targeted drugs were developed to treat HER2‐overexpressing breast cancer: lapatinib, a small‐molecule dual tyrosine kinase inhibitor that targets EGFR and HER2; trastuzumab DM1 conjugate (also known as T‐DM1), an antibody‐drug conjugate consisting of trastuzumab, a thioether ligand, and derivatives of an antimitogenic drug (maytansine); and pertuzumab, a monoclonal antibody that binds to subdomain II of the HER2 extracellular domain, thereby preventing HER2 from homologous or heterologous dimerization with other HER family receptors.256, 257, 258. The gene discussed is ERBB2; the disease is breast carcinoma.