Predictors of surgical margin status in breast-conserving surgery within a breast screening program

Background: Breast-conserving surgery (BCS) requires clear surgical margins to minimize local recurrence. We sought to identify groups of patients at higher risk of involved margins who might benefit from preoperative counselling and/or more generous excision at the first operation. Methods: We reviewed demographic, clinical, radiological and pathological records of all women diagnosed with ductal carcinoma in situ (DCIS) or invasive cancer (IC) through a population-based breast screening program in Melbourne, Australia between 1994 and 2005. Results: A total of 2,160 women were diagnosed with DCIS or IC. We excluded 199 who had mastectomy (TM) as initial procedure or had missing data. Three hundred and thirteen had a diagnostic biopsy. Of 1,648 women who had BCS after a preoperative diagnosis of DCIS or IC, 13.5% had involved margins, 16.6% had close (≤1 mm), and 69.8% clear (>1 mm) margins. Of the patients, 281/1,648 (17.1%) underwent re-excision, of whom 93 (33.1%) had residual disease identified. Mammographic microcalcifications (P < 0.0001), absence of a mammographic mass (P = 0.002), presence of DCIS (P < 0.0001), high tumour grade (P < 0.0001), large size (P < 0.0001), multifocal disease (P < 0.0001) and lobular histology (P = 0.005) were associated with involved margins. Microcalcifications (odds ratio [OR] 1.97), large size (OR 4.22) and multifocal disease (OR 2.85) were independently associated with involved margins. Residual disease was associated with involved margins (P < 0.0001), presence of DCIS (P = 0.05) and large tumour size (P = 0.01). Conclusion: After BCS, patients with mammographic microcalcifications, larger tumour size and multifocal tumours are more likely to have involved margins. Patients with involved margins, large tumour size and/or a DCIS component are more likely to have residual disease on re-excision.