A two-millimetre free margin from invasive tumour minimises residual disease in breast-conserving surgery

Aims: In breast‐conserving surgery, the width of free margin around a tumour to ensure adequate excision is controversial. The aim of this study was first to evaluate the frequency of residual disease in wider excision specimens in patients who undergo further surgery because of close margins of < 5 mm. Secondly, the ability of demographic and tumour‐related factors to predict the close margins was appraised. Patients and methods: Three‐hundred‐and‐three patients were included in the study. Patients undergoing wider excision were assessed for the presence of residual disease, and this was tested for association with the width of the initial free margin. Various factors were studied for association with close or involved margins by univariate analysis. Results: Fifty‐three per cent of patients were eligible for re‐excision based on the need for a 5‐mm clearance. With a free margin of 2 mm or more from invasive tumour, the probability of finding residual disease was 2.4%. The probability of residual disease was higher for ductal carcinoma in situ (DCIS) and did not decline with increasing the free margin width. Tumour size, lobular cancer type, vascular invasion and nodal involvement were associated with close margins. Conclusions: We suggest that a free margin of 2 mm from invasive tumour is adequate to minimise residual disease, whereas the equivalent free margin for DCIS remains unclear. Patients with large tumours and lobular cancer type should be counselled at the time of first surgery concerning the higher risk of further excision and mastectomy.