Abstract GS2-03: Prime 2 randomised trial (postoperative radiotherapy in minimum-risk elderly): Wide local excision and adjuvant hormonal therapy +/- whole breast irradiation in women =/> 65 years with early invasive breast cancer: 10 year results
Background: There is limited level 1 evidence on the long term outcomes after loco-regional radiotherapy after breast conserving surgery (BCS) in older patients when they are also receiving appropriate systemic therapy. Practice and guidelines vary. PRIME 2 is an international phase 3 RCT designed to address this specific question. Methods: From April 2003 to December 2009, 1326 patients were randomised to receive (n=658) or not receive (n=668) whole breast radiotherapy (RT). Eligible patients were aged ≥ 65 years, T1-2 (up to 3cm) NO, MO, hormone receptor positive, clear excision margins (minimum 1mm), axillary node negative (pNO) receiving adjuvant hormonal therapy. Patients were eligible if they had grade 3 tumours or lymphovascular invasion but not both. The target accrual was 1300 patients based on detecting a difference in local recurrence rates between 5% in the no RT arm and 2% in the RT arm at 5 years, with 80% power and 5% significance. Ipsilateral breast tumour recurrence (IBTR) was the primary endpoint. Secondary endpoints were regional recurrence, contralateral breast cancer, distant metastases and overall survival. Results: Median follow up is 7.3 years. At 10 years IBTR was 9.8% (95% CI 6.5, 13.2%) in the no RT arm and 0.9% (95% CI 0.1, 1.6%) in the RT arm. The hazard ratio for IBTR for those receiving RT was 0.12 (95% CI 0.05, 0.31)(p 65 years with early invasive breast cancer: 10 year results [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS2-03.