Risk factors for conversion to mastectomy due to positive margins in early breast cancer patients when choosing breast-conserving surgery: a retrospective cohort study.

Background: Breast-conserving surgery (BCS) offers oncologic safety and a superior quality of life for patients with early breast cancer (BC). However, conversion to mastectomy (CMT) owing to positive margins remains unavoidable in some cases. This study explored the risk factors contributing to this issue. Methods: This retrospective study analyzed the clinical records of patients who underwent BC surgery between January 1, 2015, and December 31, 2024. Participants were stratified into CMT and BCS groups according to the surgery they received. Demographic and clinical variables were compared between the cohorts. Potential risk factors were assessed using univariable and multivariable logistic regression, and receiver operating characteristic (ROC) curve analysis was used to assess predictive performance. Results: Among 290 patients (31 in the CMT group and 259 in the BCS group), five parameters demonstrated significant association with CMT in univariable analysis: body mass index (BMI), multifocality, tumor size, false-negative intraoperative frozen section margin, and ductal carcinoma Conclusions: Low BMI, multifocality, larger tumor size, and DCIS components independently predicted CMT in patients undergoing BCS. Although these results should be interpreted with caution, identifying these factors preoperatively may enhance surgical planning and patient outcomes.