Abstract 3688: Survival benefit of adjuvant radiotherapy among women with high comorbidity burden and low-risk breast cancer: SEER-MHOS analysis

Abstract

Abstract Background: The National Comprehensive Cancer Network Breast Cancer Guidelines Committee has suggested that adjuvant radiotherapy (RT) after breast-conserving surgery (BCS) could be omitted among older women with low-risk breast cancer (early-stage, node-negative, and ER-positive) if they were treated with endocrine therapy. However, the effect of RT among older women with multimorbidity is not clearly understood. Objective: We examined the effect of adjuvant RT on survival outcomes among older women. We also assessed whether the association between RT and survival is modified by comorbidity burden. Methods: A total of 1105 older women (65+) diagnosed with low-risk breast cancer in 1998-2012 and who received BCS were identified from the population-based Surveillance, Epidemiology, and End-Results-Medicare Health Outcomes Survey (SEER-MHOS) data resource. A propensity score-based inverse probability of treatment weight (IPTW) was calculated with weighting applied to Cox regression models to obtain hazard ratios for the association of RT with survival outcomes. Stratified analysis was conducted to examine differential effects according to the comorbidity burden class, which was identified using the latent class analysis. Results: Over a 5-year follow-up period, a total of 117 deaths occurred (25 cancer-related and 92 noncancer-related). The IPTW-adjusted Cox proportional hazard analysis showed that RT omission did not significantly increase the risk for 5-year cancer-specific deaths (P=0.202). However, RT omission increased the risk for 5-year noncancer death by 1.84-fold (95% CI=1.35, 2.51) and all-cause death by 1.49-fold (95% CI=1.41, 1.95). The stratified analysis showed that the effect of RT omission on the risk of breast cancer-specific deaths was similar across the different comorbidity groups. For noncancer and all-cause deaths, the effect of RT omission varied by comorbidity burden. In Class 1, RT omission was not associated with an increased risk of noncancer and all-cause deaths. However, in Classes 2 and 3, RT omission is significantly associated with an increased risk of 5-year all-cause deaths in a dose-response manner: by 1.66-fold (95% CI=1.07, 2.56) in Class 2 and 1.96-fold in Class 3 (95% CI=1.13, 3.41). Similar results were observed for 10-year survival. Conclusions: RT omission does not increase the risk of cancer-specific death and appears to be a valid clinical decision for older women with low-risk breast cancer and multimorbidity. Citation Format: Eunkyung Lee, Robert B. Hines, Jianbin Zhu, Kayla Montan, Michael J. Rovito. Survival benefit of adjuvant radiotherapy among women with high comorbidity burden and low-risk breast cancer: SEER-MHOS analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3688.