A Comparison of Outcomes in Early-Stage Breast Cancer After External Beam Radiotherapy, Endocrine Therapy, Both, or Neither: A Retrospective Cohort Study Across a Large Health System

Abstract

Several trials have compared endocrine therapy (ET) alone vs. ET and radiotherapy (RT) in low-risk early-stage ER+ breast cancer and have shown that the addition of RT to ET modestly reduces the rate of loco-regional recurrence (LRR) without altering survival. ET alone has thus become a standard strategy in managing these patients. Data evaluating the efficacy of RT alone is scarce. However, the toxicity of ET is not trivial, so as RT courses become ever shorter and safer, a re-evaluation of the strategy of RT alone is warranted. This analysis reports on outcomes of early-stage node-negative breast cancer treated with RT, ET, both, or neither at a multi-hospital health system. We hypothesized that RT alone yields comparable LRR to ET alone in ER+ positive early-stage breast cancer.The shared electronic health record of multiple facilities within a university health system was queried to identify women with pathologic T1-2 N0 breast cancer treated with breast-conserving surgery between 2007 and 2016. Data collection included demographic features, tumor characteristics, treatment type, and evidence of LRR. Analysis was restricted to those patients with ER+ disease. Five-year LRR were compared across groups using the Kaplan-Meier method. A multivariate analysis was performed to identify factors associated with LRR.1340 patients met inclusion criteria. Of these, 84 were treated with RT alone, 155 with ET alone, 1042 with both RT and ET, and 59 received breast conserving surgery only. Demographic and tumor variables are listed below. The 5-year rates of LRR for RT, ET, both, and neither, respectively, were 4.2% (95% CI 1.4-12.7), 5.6% (95% CI 2.6-11.7), 0.6% (95% CI 0.2-1.4), and 31.9% (95% CI 19.8-48.6). While not receiving any adjuvant therapy was associated with significantly higher rate of LRR (P < 0.001), the difference between RT and ET alone was not significant (P = .395). On multivariate analysis, age < 50 (HR 3.3; 95% CI 1.5-7.1), high grade (HR 2.5; 95% CI 1.1-5.8), and observation (HR 9.8; 95% CI 3.2-29.6) were associated with higher LRR, whereas receipt of both RT and ET was associated with lower LRR (HR 0.2; 95% CI 0.1-0.5).RT yielded LRR equivalent to ET in this population, while the combination was superior to either treatment alone. For patients with early-stage ER+ breast cancer, a prospective randomized trial comparing RT to ET and evaluating quality of life (QoL) is needed. In light of new trial data, a five-day course of RT can be considered; this treatment may yield equivalent LRR and better QoL than a five-year course of ET.