ERBB2 and breast cancer: Initially, HER‐2 was found to be an important predictor of disease progression and prognosis in breast cancer patients; subsequently, clinical trials demonstrated the efficacy of the monoclonal antibody trastuzumab, which targets an epitope on the outer structural domain of the HER‐2 protein; today, trastuzumab is widely used in the treatment of HER‐2‐positive breast cancer patients.