Abstract P2-11-01: Effects of radiotherapy on breast cancer outcomes among stage I, low-Recurrence risk, hormone-Sensitive breast cancer: Pooled analysis of individual data from phase III trials

Abstract

Purpose: Radiotherapy after breast conservation has become the standard of care. Prior meta-analyses of radiotherapy benefits pre-dated availability of gene expression profiling (GEP) to assess recurrence risk and/or did not include all relevant outcomes. This analysis utilized GEP information with individual-level data from seven clinical trials to evaluate the impact of omitting radiotherapy on recurrence and mortality. Patients and Methods: The pooled observational data included women who had undergone breast conservation surgery for stage I, ER+ and/or PR+/HER2- cancers with clinicopathologically estimated 21-Gene Recurrence Scores (RS) of ≤ 18, and did not receive chemotherapy (n= 1,684). The primary endpoint was 10-year invasive or DCIS recurrence free-interval (IRFI-DCIS), including breast cancer death and was estimated using adjusted Cox models. Secondary outcomes were breast-cancer specific and all-cause survival. Covariates included for all models were age, tumor size, grade, hormonal status, type of hormonal therapy, risk score, and trial. Results: Ten-year IRFI-DCIS was high (96.6% with radiotherapy vs. 91.6% without), for an absolute difference of 5%. Omission of radiotherapy (vs. radiotherapy) was associated with an overall adjusted hazard ratio of 2.6 (95% confidence interval 1.5-4.5) for any first event. There was only a significant increase in risk of loco-regional; not, distant recurrence, breast cancer–specific or overall survival. The effect of radiotherapy varied across subgroups, with lower first event rates for those with estimated RS of <11 (vs. 11-18), and women ages 60+ (vs. <60 years). Conclusion: Omission of radiotherapy in hormone-sensitive patients with low recurrence risk may lead to a modest absolute increase in loco-regional recurrence, but does not appear to increase risk of distant recurrence or death. Citation Format: Jayasekera JC, Schechter C, Jagsi R, White J, Chapman J-AW, Whelan T, Sparano JA, Anderson SJ, Fyles A, Sauerbrei W, Zellars RC, Li Y, Song J, Julian T, Berry D, Feuer EJ, Luta G, Mandelblatt JS. Effects of radiotherapy on breast cancer outcomes among stage I, low-Recurrence risk, hormone-Sensitive breast cancer: Pooled analysis of individual data from phase III trials [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-11-01.