The introduction of Tz therapy and, more recently, of the first successful ERBB2-targeted antibody–drug conjugate (ADC), trastuzumab emtansine (T-DM1, Kadcyla, Genentech) markedly improved the poor prognosis associated with ERBB2-amplified breast cancers [40] [41] [42]. The gene discussed is ERBB2; the disease is breast cancer.