Patients with HER2-positive breast cancer had a poor prognosis until the development of effective HER2-directed therapy, shown in randomised controlled trials (RCTs) to improve survival.1 Guidelines recommend adjuvant trastuzumab in combination with surgery, chemotherapy and radiotherapy, for patients with HER2-positive early invasive breast cancer (EIBC).2–5. The gene discussed is ERBB2; the disease is breast cancer.