We aimed to compare the prognosis of patients with close resection margins after breast-conserving surgery (BCS) with that of patients with negative margins and identified predictors of residual disease. A total of 542 patients with breast cancer who underwent BCS between 2003 and 2019 were selected and divided into the close margin (114 patients) and negative margin (428 patients) groups. The median follow-up period was 72 (interquartile range, 42-113) months. Most patients received radiation therapy (RTx) and systemic therapy according to their stage and molecular subtype. The 10-year locoregional recurrence-free survival rates of the close and negative margin groups were 88.2% and 95.5%, respectively (p = 0.001). Multivariable analysis showed that adjuvant RTx and margin status after definitive surgery were significantly associated with locoregional recurrence. Of the 57 patients who underwent re-excision, 34 (59.6%) had residual disease. Multivariable analysis revealed that a histological type of positive or close margins and multifocality were independent predictive factors for residual disease. Although the current guidelines suggest that no ink on tumor is an adequate margin after BCS, a close resection margin may be associated with locoregional failure. The treatment strategy for close resection margins after BCS should be based on individual clinicopathological features.
Keywords: breast-conserving surgery; close resection margin; locoregional recurrence; residual disease.