Comparison of Adjuvant Radiation Therapy Alone Versus Radiation Therapy and Endocrine Therapy in Elderly Women with Early-Stage, Hormone Receptor-Positive Breast Cancer Treated with Breast-Conserving Surgery

Background Randomized data examining adjuvant radiation therapy (RT) alone in elderly women with low-risk, hormone receptor-positive (HR⁺) breast cancer is lacking. We investigated the outcomes for elderly women treated with adjuvant RT alone versus RT plus endocrine therapy (ET) after breast-conserving surgery. Patients and Methods We queried our institutional breast cancer database for the following patients: age > 65 years, stage T1-T2N0, HR⁺, and treatment with breast-conserving surgery, including adjuvant RT. The χ² analysis identified significant baseline differences between the groups. Cox proportional hazard methods identified predictors of endpoints on multivariate analysis. Kaplan-Meier estimates of survival were compared using the log-rank test. Results A total of 504 patients were identified, 311 had undergone RT plus ET (62%) and 193, RT alone (38%). The median follow-up time was 88 months. The RT-alone group versus RT plus ET group had different median age (72 vs.71 years, P <.001), different median tumor size (1 vs. 1.3 cm, P <.001), lower grade (40% vs. 29%, P =.05), and fewer close or positive margins (11% vs. 19%, P =.01). The adherence rate to prescribed ET was 70%. Tumor size predicted an increased risk of distant metastasis (DM) (hazard ratio, 1.96; 95% confidence interval [CI], 1.23-3.13) and worse disease-free survival (DFS) (hazard ratio, 1.86; 95% CI, 1.22-2.86). ET nonadherence versus adherence predicted for risk of DM (hazard ratio, 5.03; 95% CI, 1.98-12.66) and DFS (HR, 4.24; 95% CI, 1.9-10.3). Of the women with DM, 83.8% had tumors > 1 cm in size. Conclusion ET nonadherence and tumor size > 1 cm predicted an increased risk of DM and worse DFS, favoring the addition of ET in this group. However, RT alone for women with tumors less than or equal to 1 cm may be appropriate.