ERBB2 and breast cancer: For T1a BC patients, adjuvant chemotherapy was ineffective for those with grade I (P = 0.43), grade II (p = 0.25), HoR + /HER2- (P = 0.75), HoR + /HER2 + (P = 0.26), and HoR-/HER2 + (P = 1).