PURPOSE

Postmastectomy radiation therapy (PMRT) improves recurrence rates and overall survival in breast cancer patients. However, it remains unclear whether these findings can be applied to human epidermal growth factor receptor 2 (HER-2) positive patients treated with trastuzumab.

METHODS AND MATERIALS

The Herceptin Adjuvant (HERA) trial is a phase III randomized clinical trial that established the efficacy of trastuzumab in HER-2 positive early stage breast cancer. The present study is a retrospective analysis of prospective data of 1633 trial patients treated with mastectomy and adjuvant trastuzumab. The primary objective of the study was to determine the effect of PMRT on loco-regional recurrence rates (LRR). Hazard ratios were estimated from Cox models, and LRR curves were generated by the Kaplan-Meier method.

RESULTS

Our analysis included 940 patients (57.6%) who received PMRT and 693 patients (42.4%) who did not. Patients in the PMRT group had worse prognostic disease characteristics. At a median follow-up of 11 years, no significant difference in LRR was noted after PMRT in node negative (N0) patients (P = .96). Patients with 1 to 3 positive lymph nodes had a LRR-free survival of 97% in the PMRT group compared with 90% in the no PMRT group (hazard ratio = 0.28, P = .004) and a nonsignificant improved overall survival after PMRT (hazard ratio = 0.63, P = .06).

CONCLUSIONS

PMRT delivery in HER-2 positive breast cancer patients with 1 to 3 positive lymph nodes decreases the risk of LRR. Although the magnitude of PMRT benefit is lower than historic studies, the present findings are in favor of PMRT for HER-2 positive breast cancer patients with 1 to 3 involved nodes. Future studies are needed to determine which HER-2 positive breast cancer patients benefit the most from PMRT.