Regional nodal irradiation after breast conserving surgery for HER2-positive breast cancer: Results of a sub analysis from the ALTTO trial

604Background: The optimal treatment of regional nodal areas following breast-conserving surgery (BCS) is a source of debate. Two randomized trials recently demonstrated that regional nodal irradiation (RNI) can reduce the risk of recurrence in early breast cancer; however,these trials were conducted in the pre-trastuzumab era.Whether these results are applicable to HER2-positive breast cancer patients treated with anti-HER2 targeted therapy, is unknown. Methods: This retrospective analysis was performed on patients with node-positive breast cancer, who were enrolled in the ALTTO phase III adjuvant trial and subjected to BCS. The primary objective of the present study was to examine the effect of RNI on disease-free survival (DFS). Secondary objectives included regional recurrences and overall survival (OS). A multivariate cox regression analysis adjusted for number of positive lymph nodes, tumor size, grade, age, hormone receptors status, presence of macrometastatis, treatment arm, and chemotherapy timin...