ERBB2 and breast cancer: Because of the phenomenal success of treatment with monoclonal antibodies and antibody‐drug conjugates targeting human epidermal growth factor receptor 2 (HER2), most patients with early‐stage HER2‐positive breast cancer (HER2+ BC) and some with limited metastatic diseases have been cured, and those who have not been cured have achieved significant improvements in overall survival, which has weakened the role of the TNM staging system in the prognosis of HER2+ BC today.