Supplementary Material for: Clinicopathological Factors Affecting Positive Margins after Breast-Conserving Surgery: A Comparative Study of Low- and High- Volume Hospitals.

Purpose: Positive margins after breast-conserving surgery (BCS) are an important risk factor for local tumor recurrence and the need for re-excision in women with breast cancer. It remains unclear which factors collectively influence positive margins after BCS and whether the outcomes vary among hospitals. This study investigated the occurrence and risk factors of positive margins after BCS in women with breast cancer in two Dutch hospitals.
Methods: Data was collected retrospectively from medical records of women who were diagnosed with newly invasive breast carcinoma or carcinoma in situ and underwent primary BCS between January 1, 2018 and December 31, 2020 in two Dutch hospitals.
Results: A total of 423 cases (410 patients) were included, with a median age of 58 years (IQR 51-66). On average the positive margin rate after BCS was 8.0%, which was significantly higher in the low-volume hospital (14.9%) than in the high-volume hospital (5.9%). Invasive lobular carcinoma (OR= 4.97, CI= 1.91 – 12.94), postoperative tumor size (OR= 1.07, CI= 1.03 – 1.11), low hospital volume (OR= 3.90, CI= 1.58 – 9.66), and lumpectomy size (OR= 0.97, CI= 0.94 – 1.00) were significantly associated with positive margins after BCS.
Conclusion: Positive margin rate after BCS was low with 8.0% among all cases and varied significantly between the hospitals. Patient-, tumor-, radiological- and surgery-related factors may contribute to these variations. An optimized collaborative multidisciplinary approach to breast cancer care, particularly between radiologists and surgeons, should be strived to achieve improved oncological outcomes in women after BCS.