New Findings on Margins in DCIS

Current consensus recommendations for margins in DCIS patients treated with breast conservation are based on the 2016 SSO/ASTRO/ASCO Guidelines. These guidelines were developed by a multidisciplinary panel after comprehensive systematic review and meta-analysis of existing data for guidance of appropriate margins. This multidisciplinary expert panel concluded that a ≥2mm margin is associated with a lower risk of ipsilateral recurrence compared to <2mm margins. However, current recommendations do recognize the importance of individualized clinical decision making, particularly in cases of small volume disease with closer margins.

The recent publication by Wapnir et al. has prompted reconsideration of the existing guidance. Wapnir et al. published results from an ancillary analysis of margin status within the larger NRG Oncology/NSABP B-35. This phase 3 randomized controlled trial compared adjuvant treatment with tamoxifen versus anastrozole in postmenopausal women with hormone receptor positive DCIS undergoing breast conserving surgery, adjuvant whole breast irradiation (WBI), and endocrine therapy. Margin width was prospectively collected and classified as having tumor on ink (positive), a margin <1mm (close margin), or ≥1mm (negative margin). For the ancillary analyses, the negative margin group was further subdivided and dichotomized as <1 vs ≥1mm and <2 vs ≥2mm margins. Patients having a positive margin (tumor on ink) were excluded from the analysis. Among the 2707 patients, 98.7% received WBI and 82% received an additional boost. The 10-year unadjusted cumulative incidence of ipsilateral breast tumor recurrence (IBTR) rates remained low across all groups, though with statistically significant differences (5.6% for <1mm and 4.0% for ≥1mm; 5.3% for <2mm and 3.8% ≥2mm). The 10-year absolute difference in IBTR incidence was only 1.6% for those with ≥1mm vs. <1mm margins; and 1.5% in those with ≥2mm vs. <2mm margins. Furthermore, in adjusted analyses, inclusive of patient and clinical characteristics, margin width was not associated with tumor recurrence.

Given the strength of evidence and with adjusted models showing no difference in local recurrence rates with greater margins, routine surgical re-excision of close margins deserves reconsideration in postmenopausal women with hormone receptor positive DCIS undergoing breast conserving surgery, whole breast radiation, and endocrine therapy.

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