ERBB2 and breast cancer: In the recent eighth edition of the American Joint Committee on Cancer (AJCC) staging system for BC, the prognostic-stage groups showed that patients with HER2-positive tumors tended to be grouped into a lower stage than patients with HER2-negative tumors provided that other staging factors were identical because most of the patients used to generate the eighth edition of the AJCC staging system in the initial models received trastuzumab (26).