Human epidermal growth factor receptor 2 (HER2)-directed therapy (HER2-Tx) with drugs such as trastuzumab has revolutionized the treatment of HER2-positive breast cancer but with a black box warning of cardiotoxicity.1 Most of the time, this is in form of a decline in cardiac function whereas heart failure is rare (∼15–20% and <5% of patients, respectively). The gene discussed is ERBB2; the disease is breast cancer.