In the case of HER2+ breast cancer, the monoclonal antibody trastuzumab (Herceptin) and its cytotoxic drug-conjugated derivative trastuzumab-emtansine (Kadcyla), the monoclonal antibody blocking HER2-HER3 dimerisation pertuzumab (Perjeta), and the small molecule kinase inhibitor lapatinib (Tykerb/Tyverb) have been successful in the clinic (Blackwell et al., 2010; Cameron et al., 2017; Diéras et al., 2017; Geyer et al., 2006; Krop et al., 2017; CLEOPATRA Study Group et al., 2015; EMILIA Study Group et al., 2012). The gene discussed is ERBB3; the disease is breast cancer.