Impact of whole breast irradiation, endocrine therapy or their combination on outcomes of early-stage, luminal A-like, low-risk, breast cancer patients aged 65 years or over: Insights from the EUSOMA database

Aim: To assess oncological outcomes in early-stage, luminal A-like, low-risk, breast cancer patients aged 65 years or more after conserving surgery followed by endocrine therapy (ET) and/or whole breast irradiation (WBI) or no adjuvant therapy. Methods: Data from patients treated in EUSOMA-certified breast units between 2010 and 2022 were collected. Univariable and multivariable analyses for local, nodal, distant recurrences, breast cancer specific survival (BCSS), and overall mortality were conducted. Potential treatment-related determinants included adjuvant ET alone, WBI alone, ET+WBI or no adjuvant therapy. Results: Breast cancer patients (9660) from 72 Breast Units across 14 European countries were enrolled. Tumours were pT1 in 85.8 % of cases. All tumours were luminal A-like. All patients had negative nodes. Adjuvant ET alone was prescribed for 806 (8.3 %) and WBI alone was delivered to 386 (4.0 %); ET and WBI were combined (ET+WBI) in 8154 (84.4 %) patients. No adjuvant therapy was given to 314 patients (3.3 %). The median follow-up was 1.87 years (first quartile 0.81, third quartile 4.16), and the mean was 2.62 years (range 0.003-13.82 years). Compared with no adjuvant therapy, multivariable analysis showed ET+WBI significantly improved in-breast tumour recurrence-free survival (IBTRFS) (HR 0.28, CI 95 % 0.10 -0.79; p = 0.016) and BCSS (HR 0.12; CI 95 %: 0.03 -0.51; p = 0.004). ET alone (HR 0.57; CI 95 %: 0.35 -0.90; p = 0.017), WBI alone (HR 0.51; CI 95 %: 0.27 -0.95; p = 0.033) and both treatments combined (HR 0.26; CI 95 %: 0.16 -0.42; p < 0.001) significantly lowered mortality. Conclusions: Despite a short follow-up, results from this large series of low-risk breast cancer patients who had undergone conserving surgery, showed adjuvant treatments impacted positively upon outcomes.