Adjuvant breast radiotherapy, endocrine therapy after breast conserving surgery in older women with low-risk breast cancer: Results from a population-based study.

BACKGROUND AND PURPOSE The relative benefit of adjuvant radiotherapy (RT) alone in older women with low-risk early breast cancer (EBC) remains unclear. It is hypothesised that adjuvant RT-alone can improve outcomes of older patients with low-risk EBC, similar to endocrine therapy (ET) alone or combination of RT+ET. METHODS In this population based study, we identified all women aged ≥70 with T1-2, N0, ER+ve, Her-2/neu-ve EBC treated with breast conserving surgery (BCS), followed by adjuvant treatment (RT-alone, ET-alone, or RT+ET combination) from 2005 to 2015. Primary outcome measures were recurrence-free survival (RFS), overall survival (OS), and breast cancer specific survival (BCSS). Treatment details were collected and Charlson Comorbidity Index (CCI) was calculated. RESULTS A total of 1166 patients were identified. Median follow-up was 76.5 months. Adjuvant treatments: BCS only 130 (11%), RT 378 (32.5%), ET 161 (14%), and RT+ET 497 (42.5%). Less than 60% of women completed 5-years ET. Compared to BCS alone, RT resulted in significant improvement in RFS (HR=0.174; p<0.001), similar to ET (HR=0.414; p=0.007) and RT+ET (HR=0.236; p<0.001). Determinants of OS were age, tumor grade, comorbidities, and adjuvant therapy. Increased comorbidity scores (0 vs. 1; 0 vs. ≥2) were associated with reduced OS (HR=1.40; p=0.013 and HR=1.98; p<0.001), without impact on RFS or BCSS. CONCLUSIONS Adjuvant RT-alone is a reasonable alternative to ET or RT+ET for older women with biologically favourable EBC. No difference in RFS or BCSS was noted between RT, ET, and RT+ET. Comorbidity was independently associated with reduced overall survival.