Trastuzumab Provides a Comparable Prognosis in Patients With HER2-Positive Breast Cancer to Those With HER2-Negative Breast Cancer: Post Hoc Analyses of a Randomized Controlled Trial of Post-Mastectomy Hypofractionated Radiotherapy.

BACKGROUND AND PURPOSE: We investigated the locoregional effect of trastuzumab, and determined whether patients with human epidermal growth factor receptor (HER)2-positive breast cancer (BC) treated with trastuzumab could achieve comparable efficacy to that of patients with HER2-negative BC. MATERIALS AND METHODS: This was post hoc analyses of data of 793 BC patients from a randomized controlled trial comparing post-mastectomy hypofractionated radiotherapy with conventional fractionated radiotherapy. Survival rates were analyzed by the Kaplan-Meier method and compared by the log-rank test. RESULTS: Patients were classified into three groups: HER2-negative (HER2-; n = 547), HER2-positve with trastuzumab (HER2+ + T; n = 136), and HER2-positive without trastuzumab (HER2+ - T; n = 110). The HER2+ + T group had significantly lower locoregional recurrence (LRR, 6.0% vs. 13.9%), distant metastasis (DM, 17.4% vs. 33.8%) and higher disease-free survival (DFS, 81.2% vs. 61.9%) at 5 years than that of the HER2+ - T group (P <.05). The HER2- group had significantly lower LRR (6.8% vs. 13.9%), DM (22.4% vs. 33.8%) and higher DFS (76.1% vs. 61.9%) at 5 years than that of the HER2+ - T group (P <.05). The difference in LRR, DM and DFS at 5 years was not significant between the HER2+ + T group and HER2- group (P >.05). Different annual LRR patterns was found among groups according to HR status. CONCLUSION: Trastuzumab reduces LRR in patients with locally advanced HER2-positive BC who have received post-mastectomy radiotherapy. It provides comparable DFS to that with patients with HER2-negative BC.