Approximately 15–20% of breastcancers (BC) are classifiedas human epidermal growth factor receptor-2 (HER2)-positive.1 HER2-positive BC was historically associatedwith a poor prognosis.2 However, patientoutcomes have improved over recent years due to the introduction ofHER2-targeted therapies such as trastuzumab (Herceptin, Roche) andpertuzumab (Perjeta, Roche).3 Nonetheless,resistance to HER2-targeted therapies remains a challenge. Here, ERBB2 is linked to breast cancer.