Adjuvant Radiation vs Endocrine Therapy After Lumpectomy for Early-Stage Breast Cancer in Older Women: Analysis of Real-World Survival Outcomes

Background. We examined whether adjuvant radiation therapy (RT) monotherapy offers comparable overall survival (OS) to adjuvant endocrine therapy (ET) monotherapy following lumpectomy in women aged >= 65 years with favorable early stage breast cancer. Patients and Methods. Patients aged >= 65 years, diagnosed with ER+/HER2-, cT1-2, N0 breast cancer, who underwent lumpectomy, were selected from the National Cancer Database (2004-2020). Kaplan-Meier estimates and Cox Proportional Hazards models evaluated OS differences across RT-only and ET-only groups. Results. The final cohort included 91,505 patients, with 11.8% receiving RT alone and 29.5% receiving ET only. Median follow-up was 67.6 months. ET-only patients were less likely to have a comorbidity score of 0 (ET 75.4% versus RT 80.8%; p < 0.001). Patients in the ET-only group had slightly larger tumors [ET 1.0 cm (0.7-1.5 cm) versus RT 0.9 cm (0.6-1.3 cm); p < 0.001] and were less likely to have grade 3 tumors (ET 7.0% versus RT 8.4%; p < 0.001). Unadjusted Kaplan-Meier analysis showed a higher 5 year OS for RT-only patients compared with ET-only (RT 88.9% versus ET 85.8%; p < 0.001). A similar trend was observed when stratified on the basis of age group (all log rank p < 0.05). In the adjusted multivariable analysis, RT-only remained associated with a slightly better OS than ET-only [ET ref, RT hazards ratio 0.91 (95% CI 0.85-0.97)]. Conclusions. For older patients with early stage, ER+/HER2- breast cancer who undergo lumpectomy, patients receiving RT-only had a small survival advantage over patients receiving ET-only, which may or may not be clinically relevant. Further comparisons of RT-only versus ET-only may be warranted in this unique population.