ESTRO 2025 - Abstract Book

S606

Clinical - Breast

ESTRO 2025

At a median follow-up of 8.2 years (IQR 4.8–12.7) after diagnosis, 924 (19%) patients experienced LorC BC, 572 (12%) a distant recurrence, 190 (4%) a second primary non-BC, and 35 (1%) a death without recurrence. The 7-year cumulative incidence of LorC BC was 19%, 13%, and 10% in patients treated with BCS+RT, mastectomy alone, and mastectomy+RT, respectively. Compared to mastectomy alone, BCS+RT was associated with a higher incidence of LorC BC events (unadjusted subdistribution HR [sHR] 1.80, 95% CI 1.53–2.11), while a similar incidence of LorC BC events was observed with mastectomy+RT (unadjusted sHR 0.84, 95% CI 0.69–1.02). However, no significant differences were observed after adjusting for uptake of bilateral risk-reducing mastectomy and other prognostic factors (adjusted sHR 1.09, 95% CI 0.90–1.31 for BCS+RT and 0.82, 95% CI 0.66–1.02 for mastectomy+RT). In subgroup analyses, a significant interaction was identified between primary tumour treatments and specific BRCA mutations, with BRCA1 carriers treated with BCS+RT showing a higher risk of LorC BC.