ERBB2 and breast cancer: We aimed to determine whether: (i) adjuvant trastuzumab reduced locoregional recurrence (LRR) in patients with stage-II and III BC (according to AJCC 7th edition) treated with post-mastectomy radiotherapy; (ii) patients with HER2-positive BC treated with trastuzumab had comparable outcomes to those of patients with HER2-negative BC.