Adjuvant radiotherapy alone, an effective treatment option for early-stage low- risk breast cancer in women over 50: results from a population based cohort study using a Canadian provincial database.

Abstract

Breast conserving surgery (BCS) is the primary treatment for early-stage breast cancer(EBC). Typically, adjuvant endocrine therapy (ET) and radiation therapy (RT) are standard treatments offered for EBC. However, non-compliance and toxicity remain as issues with HT and many patients choose adjuvant RT alone. The benefit of adjuvant RT alone in women with low-risk EBC remains unclear. It is hypothesized that adjuvant RT-alone can improve outcomes in low-risk EBC patients, similar to ET alone or RT + ET combination. This population-based study identified women aged 50-80 with T1, N0, Estrogen receptor positive (ER + ve), human epidermal growth receptor-2 negative(Her-2/neu-ve) EBC treated with BCS, followed by adjuvant treatments (RT-alone, ET-alone, or RT + ET combination) from 2010 to 2015. Primary outcomes were recurrence free survival (RFS), overall survival (OS), and breast cancer specific survival (BCSS). 2810 patients were identified. Median follow-up was 73 months(Interquartile Q₁,Q₃:55.0,91.6). Adjuvant treatments were: BCS only 216 (8 %), RT alone 803 (29 %), ET alone 274 (10 %), and RT + ET combination 1517 (54 %). 398 patients (22.2 %) completed 5-years of ET. Compared to BCS alone, there was no statistically significant difference between treatment groups for RFS and BCSS. There were significant difference among the treatment groups for OS compared to BCS alone: Hazard ratio (HR) 0.66 (95 % confidence interval (CI): 0.45 - 0.97) for RT alone, 0.55 (95 % CI: 0.35 - 0.87) for ET alone, and 0.48 (95 % CI: 0.33 - 0.70) for RT + ET combination. Determinants of OS were age, tumor grade, comorbidities, and adjuvant therapy. Our population-based cohort study showed that there was no statistically significant difference in RFS and BCSS among various adjuvant treatments versus BCS alone. However, RT alone, ET alone and RT + ET combination resulted in a statistically significant improvement in OS compared to BCS alone. Our findings support RT alone can be a viable alternative to ET + RT combination for women over 50 with low-risk EBC. Ongoing studies like EUROPA, REaCT trial and EPOPE will provide more insight into the role of RT alone as a definite treatment option.