Abstract P2-10-05: Survival in Older Women Receiving Adjuvant Radiation Monotherapy vs. Endocrine Monotherapy Following Lumpectomy

Background: Breast cancer is increasingly prevalent in women over 65, and most are diagnosed with hormone receptor positive disease. While younger patients with early-stage breast cancer are treated with both adjuvant radiation therapy (RT) and endocrine therapy (ET), many clinical trials have shown that omitting radiation among older patients who take adjuvant ET does not decrease survival. However, ET is difficult for many older patients to tolerate, and some may prefer a short course of RT monotherapy instead of ET. While ET can reduce both local and distant recurrence risk, older women with favorable breast cancers may have a sufficiently low distant recurrence risk that omission of ET may be reasonable, if RT is given to reduce local recurrence. Therefore, the aim of this study was to determine whether treatment with adjuvant RT monotherapy results in comparable overall survival (OS) to treatment with adjuvant ET monotherapy in women age ≥65 diagnosed with favorable early-stage breast cancer. Methods: Patients aged ≥65, diagnosed in 2010-2020 with ER+/HER2-, prognostic clinical stage I breast cancer (cT1-2, N0), who underwent lumpectomy, were selected from the National Cancer Database. Patients who received any chemotherapy and/or any neoadjuvant therapy were excluded. Differences across groups were tested. The Kaplan-Meier method was used to estimate OS, and log-rank tests were used to test for differences in OS between groups. Stratified analyses were conducted based on age group (65-69, 70-74, 75-79, 80+). A Cox Proportional Hazards model was used to estimate the association of the treatment group with overall survival after adjustment for available covariates. Results: The final cohort included 91,505 patients, with 13.5% receiving no adjuvant therapy, 11.8% receiving RT alone, 29.5% receiving ET only, and 45.2% receiving both RT and ET. The median follow-up for the entire cohort was 67.6 months. Patients in the RT-only and ET-only groups were of similar age [median (IQR): RT 73yo (69-79) vs ET 75yo (71-80); p<0.001], although patients in the ET-only group were less likely to have a comorbidity score of 0 (ET 75.4% vs RT 80.8%; p<0.001). Patients in the ET-only group had minimally larger tumors [median tumor size (IQR): ET 1 (0.7-1.5) vs RT 0.9 (0.6-1.3); p<0.001], were less likely to have grade 3 tumors (ET 7.01% vs RT 8.38%; p<0.001), and were slightly more likely to have PR+ disease (ET 91.4% vs RT 89.6%; p<0.001). In the unadjusted Kaplan-Meier analysis, patients receiving ET-only had a slightly lower 5-year OS compared to the RT-only group [ET 85.8% (85.3-86.3%) vs RT 88.9% (88.2-89.6%); log rank p<0.001]. A similar trend was observed when stratified based on age group, although notably less pronounced (all log rank p<0.05). In the adjusted multivariable analysis, RT alone remained associated with a slightly better OS than ET alone [ET ref, RT hazards ratio 0.91 (95% CI 0.85-0.97)]. Conclusions: For older patients with early-stage, ER+/HER2- breast cancer, survival outcomes were largely similar for those who received adjuvant RT monotherapy vs adjuvant ET monotherapy. While prior studies have evaluated de-escalation of radiotherapy, de-escalation of endocrine therapy has not been as extensively explored. Direct comparisons of RT alone vs ET alone may be warranted in this unique population with variable life expectancy and potentially different treatment preferences.Citation Format: Tori Chanenchuk, Kerri-Anne Crowell, Ton Wang, Laura H. Rosenberger, Gayle A. DiLalla, Susan G. R. McDuff, Gretchen Kimmick, E. Shelley Hwang, Jennifer K. Plichta. Survival in Older Women Receiving Adjuvant Radiation Monotherapy vs. Endocrine Monotherapy Following Lumpectomy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-10-05.

Duke Scholars

Author Jennifer K Plichta Surgical Oncology

Author Gayle Ackerman DiLalla Surgical Oncology