Top Line: What is considered an adequate margin for DCIS?
The Study: A 2016 SSO/ASTRO/ASCO consensus panel recommended at least 2 mm margins for DCIS based largely on a meta-analysis of 20 studies with over 7000 patients treated with lumpectomy and whole-breast irradiation. It found a lower risk of ipsilateral recurrence when margins were >2 mm when compared with thresholds of >0 mm and >1 mm. No randomized trials have evaluated specific DCIS margins. Most of the landmark trials (NSABP B-17, B-24, SweDCIS, EORTC 10853) either did not require tumor-free margins or simply defined margins as tumor free without specifying width, and RTOG 9804 required ≥3 mm for eligibility. This NCDB analysis evaluated over 11,000 patients who had breast conservation for DCIS. Of these, 38.6% had high grade disease and 81.5% were hormone receptor positive. Most patients (72%) received adjuvant radiation, and 43% received endocrine therapy. Most (53.6%) had >2 mm margins, 5.8% had 1-1.9 mm margins, 24.4% had 0.01-0.9 mm margins, and 16.2% had positive margins. Among those who received RT, recurrence was lower for those with >2 mm margins than those with positive margins (4.4% v 2%). However, the differences between narrower margin thresholds was not significant. The same was also true among those who did not receive RT, granted their rates of recurrence were higher than with adjuvant RT. One exception was the subgroup of younger patients (<50) who had lower recurrence risk with >2 mm margins compared with closer negative margins.
TBL: This NCDB analysis found that close but negative margins were not associated with increased recurrence risk compared with >2 mm margins. An exception, though, was patients <50 who had lower risk with wider margins. | Nash, J Clin Oncol 2026
The Study: A 2016 SSO/ASTRO/ASCO consensus panel recommended at least 2 mm margins for DCIS based largely on a meta-analysis of 20 studies with over 7000 patients treated with lumpectomy and whole-breast irradiation. It found a lower risk of ipsilateral recurrence when margins were >2 mm when compared with thresholds of >0 mm and >1 mm. No randomized trials have evaluated specific DCIS margins. Most of the landmark trials (NSABP B-17, B-24, SweDCIS, EORTC 10853) either did not require tumor-free margins or simply defined margins as tumor free without specifying width, and RTOG 9804 required ≥3 mm for eligibility. This NCDB analysis evaluated over 11,000 patients who had breast conservation for DCIS. Of these, 38.6% had high grade disease and 81.5% were hormone receptor positive. Most patients (72%) received adjuvant radiation, and 43% received endocrine therapy. Most (53.6%) had >2 mm margins, 5.8% had 1-1.9 mm margins, 24.4% had 0.01-0.9 mm margins, and 16.2% had positive margins. Among those who received RT, recurrence was lower for those with >2 mm margins than those with positive margins (4.4% v 2%). However, the differences between narrower margin thresholds was not significant. The same was also true among those who did not receive RT, granted their rates of recurrence were higher than with adjuvant RT. One exception was the subgroup of younger patients (<50) who had lower recurrence risk with >2 mm margins compared with closer negative margins.
TBL: This NCDB analysis found that close but negative margins were not associated with increased recurrence risk compared with >2 mm margins. An exception, though, was patients <50 who had lower risk with wider margins. | Nash, J Clin Oncol 2026