Margin width and local recurrence after breast conserving surgery for ductal carcinoma in situ

INTRODUCTION: Ductal Carcinoma in situ (DCIS) represents 5% of symptomatic and 20-30% of screen detected cancers. Breast conserving surgery (BCS) ± radiotherapy is performed in over 70% of women with DCIS. What constitutes an adequate margin for BCS remains unclear.

METHODS: A single institution follow up study has been conducted of 466 patients with pure DCIS treated by BCS between 2000 and 2010 of whom 292 received whole breast radiotherapy and 167 did not. Patients were selected for radiotherapy based on perceived risk of in breast tumour recurrence (IBTR). Distance to nearest radial margin was measured; 10 patients had a margin width of <1 mm, 94 had widths of 1-2 mm and 362 had widths of >2 mm. There was no association of margin width and the use of radiotherapy.

RESULTS: At a median follow up of 7.2 years there were 44 IBTR (27 DCIS and 17 invasive). There was no evidence that margin widths >2 mm resulted in a lower rate of IBTR than margin widths of 1-2 mm. The actuarial IBTR rates at 5 and 10 years for margins of 1-2 mm were 9.0% (95% CI ± 5.9%) and 9.0% (95% CI ± 5.9%) respectively and for margins of >2 mm were 8.0% (95% CI ± 3.9%) and 13.0% (95% CI ± 3.9%) respectively. Odds Ratio for IBTR 1-2 mm vs >2 mm was 0.839 (95% CI 0.392-1.827) p = 0.846. In a multivariate analysis only DCIS size predicted for IBTR (HR 2.73 p < 0.0001).

CONCLUSION: 1 mm appears a sufficient margin width for BCS in DCIS irrespective of whether patients receive radiotherapy.