As our understanding of the effects of ET on HR+ breast cancers is largely restricted to the use of actively growing tumours or cell lines, there is an urgent need for more clinically relevant models (such as rapid autopsy studies, described below) to reveal how DTCs respond to hormone therapy, or to other targeted treatments (e.g., HER2-directed therapy for HER2+ breast cancers). The gene discussed is ERBB2; the disease is neoplasm.