Abstract S2-01: The PRIME II trial: Wide local excision and adjuvant hormonal therapy ± postoperative whole breast irradiation in women ≥ 65 years with early breast cancer managed by breast conservation

Abstract

Abstract Background. Local Recurrence rates after breast conserving surgery (BCS) are falling because of increasing use of effective systemic therapy. The question of whether whole breast radiotherapy (WBRT) can be omitted in carefully defined groups of older patients receiving appropriate systemic therapy has not been addressed. PRIME II is an International phase III RCT addressing this question. Methods. Between April 2003 and December 2009, 1326 patients were randomised to receive (n = 658) or nor receive (n = 668) radiotherapy (RT). Eligiblity criteria were ≥65 years, T1-2 (up to 3cm), N0, M0, hormone receptor positive, clear excision margins (≥ 1mm), axillary node negative women in receipt of adjuvant hormone therapy. Patients could have Grade 3 tumours or lympho-vascular invasion but not both. An accrual of 1300 was planned to detect a difference based on estimates of local recurrence of 2% in RT group and 5% in no RT arm at 5 years, with 80% power and 5% significance. The primary endpoint was ipsilateral breast tumour recurrence (IBTR). Secondary endpoints were regional recurrence, contralateral breast cancer, distant metastases and overall survival (OS). Median follow up is 5.0 years. Results IBTR at 5 years was 4.1% (95% CI 2.4, 5.7%) without RT, 1.3% (95% CI 0.2, 2.3%) with RT. The hazard ratio for IBTR in those IBTR receiving radiotherapy was 4.34 (1.79, 10.55) (p = 0.001). Overall actuarial survival at 5 years was 93.8% (95% CI 91.6, 95.9%) without RT and 94.2% (95% CI 92.2, 96.3%) with RT, (p = 0.24). No significant differences in regional recurrence (1.4% no RT vs 0.5% RT), contralateral breast cancer (0.9% no RT vs 1.5% RT), nor distant metastases (1.0% vs 0.3%) were seen. Breast cancer-free survival was 94.6% (95% CI 92.7, 96.5%)for no RT and 97.3% (95% CI 95.9, 98.8%) for those receiving RT (p = 0.003): this difference was due to the greater IBTR in no RT group. The majority of deaths were not linked to breast cancer (35 no RT vs 29 RT from a total of 87 deaths), with no influence of omission of RT (p = 0.27). Conclusions The randomised International Trial has shown that • Omission of RT in women ≥65 year of age with N0, ER positive breast cancer receiving endocrine therapy results in only a 4.1% 5 year IBTR • Although RT reduces IBTR significantly, the absolute reduction in this study is very small. • RT does not reduce the rate of regional recurrence, distant metastases or affect overall survival. • Omission of postoperative WBRT in this population based on the 5 year rate of IBTR appears safe, especially in the presence of comorbidities. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S2-01.