Stereotactic ablative radiotherapy for oligometastatic breast cancer: A systematic review and meta-analysis (SABRINA).

Abstract

Stereotactic ablative radiotherapy (SABR) is increasingly used for oligometastatic breast cancer, but it is unclear in whom local ablation translates into systemic benefit. We compared de novo oligometastatic (OM) with oligoprogressive (OP) disease and synthesised randomised evidence. PubMed, EMBASE, Cochrane CENTRAL and ClinicalTrials.gov were searched through March 2026. Endpoints were local control (LC), progression-free survival (PFS), overall survival (OS), time to next systemic therapy (TTNS) and grade 3 or higher adverse events. Proportions were pooled by random-effects models, adverse events by a binomial-normal model accommodating zero-event studies, and trials separately. Twenty-five cohorts (1,577 patients; 2,211 lesions) were included. Pooled LC was 92.5 % (95 % CI 90.4-94.2) at one year and 84.6 % (81.1-87.6) at two years, with no association with BED₁₀. At two years, PFS was 43.1 % (34.4-52.2) and OS 85.8 % (76.0-92.0). Outcomes were consistently superior in de novo OM than in OP: LC 95.7 % versus 88.9 % (p = 0.001), PFS 50.9 % versus 30.9 % (p = 0.003), OS 91.0 % versus 65.8 % (p = 0.002), and TTNS 18.5 versus 11.3 months. Within OP, lesion number was independently associated with TTNS (adjusted HR 1.77 per lesion). Across four randomised trials the pooled hazard ratio for PFS was 0.73 (0.53-1.00; p = 0.053). Grade 3 or higher adverse events occurred in 21 of 1,366 patients (1.50 %; 0.74-2.28). SABR achieves durable local control with few treatment-related adverse events in all clinical contexts. Clinical context, rather than dose or metastatic site, determines whether that local effect translates into systemic benefit. Randomised evidence neither establishes nor excludes a benefit; trials stratified by oligometastatic state are required.