doi:10.1016/j.suronc.2026.102369engOtero-Romero, DanielArribas-del-Amo, DoloresThe modified 5-item frailty index predicts long-term mortality after breast cancer surgery in elderly women: A five-year follow-up studyART-2026-148314Purpose: Frailty is a major determinant of outcomes in older adults with cancer, and its identification in surgical oncology patients provides an opportunity to enhance perioperative care. However, the association of frailty with long-term outcomes remains poorly characterized. This study evaluated the prognostic value of the modified 5-item frailty index (mFI-5) in predicting long-term survival among elderly women undergoing breast cancer surgery. Methods: A retrospective observational study was conducted including 290 women aged ≥70 years who underwent breast cancer surgery between 2016 and 2021. Frailty was assessed using the mFI-5 and categorized as fit (score = 0), pre-frail (score = 1), and frail (score ≥2). Long-term survival rates were analyzed across age groups, tumor subtypes, and TNM stages, stratified by mFI-5 category. Results: Frailty was identified in 37.2% of patients and was strongly associated with reduced long-term overall survival (52.6% in frail vs. 88.4% in fit patients at 5 years). Multivariable Cox regression confirmed frailty as an independent predictor of mortality (HR 3.14, p = 0.003), primarily driven by non-cancer related deaths. The prognostic performance of the mFI-5 was consistent across all subgroups analyzed. Conclusion: The mFI-5 is a simple and practical tool that identifies elderly women with breast cancer at increased risk of long-term mortality following surgery. Incorporating the mFI-5 into routine preoperative evaluation may facilitate improved treatment planning and outcomes.2026http://zaguan.unizar.es/record/16937410.1016/j.suronc.2026.102369http://zaguan.unizar.es/record/169374oai:zaguan.unizar.es:169374SURGICAL ONCOLOGY-OXFORD 65 (2026), 102369 [6 pp.]by-nc-ndhttps://creativecommons.org/licenses/by-nc-nd/4.0/deed.esinfo:eu-repo/semantics/embargoedAccess