Endocrine therapy with or without whole breast irradiation in low-risk breast cancer patients after breast-conserving surgery: 10-year results of the Austrian Breast and Colorectal Cancer Study Group 8A trial

Purpose: To investigate long-term results of patients with hormonal receptor epositive breast cancer treated with breast-conserving surgery (BCS) and consecutive endocrine therapy (ET) with or without whole breast irradiation (WBI). Methods and materials: Within the 8 A trial of the Austrian Breast and Colorectal Cancer Study Group, a total of 869 patients received ET after BCS which was randomly followed by WBI (n = 439, group 1) or observation (n = 430, group 2). WBI was applied up to a mean total dosage of 50 Gy (+/- 10 Gy boost) in conventional fractionation. Results: After a median follow-up of 9.89 years, 10 in-breast recurrences (IBRs) were observed in group 1 and 31 in group 2, resulting in a 10-year local recurrenceefree survival (LRFS) of 97.5% and 92.4%, respectively (p = 0.004). This translated into significantly higher rates for disease-free survival (DFS): 94.5% group 1 vs 88.4% group 2, p = 0.0156. For distant metastasese free survival (DMFS) and overall survival (OS), respective 10-year rates amounted 96.7% and 86.6% for group 1 versus 96.4% and 87.6%, for group 2 (ns). WBI (hazard ratio [HR]: 0.27, p < 0.01) and tumour grading (HR: 3.76, p = 0.03) were found as significant predictors for IBR in multiple cox regression analysis. Conclusions: After a median follow-up of 10 years, WBI resulted in a better local control and DFS compared with ET alone. The omission of WBI and tumour grading, respectively, were the only negative predictors for LRFS. (C) 2019 Elsevier Ltd. All rights reserved.