DCIS MARGINS: DO WE NEED TO RE-EXCISE EVERY MARGIN

An important new analysis from the NRG Oncology/NSABP B-35 randomized clinical trial, published in JAMA Surgery, challenges how rigidly we should apply margin-width thresholds in selected patients with ductal carcinoma in situ (DCIS).

Wapnir and colleagues evaluated the association between lumpectomy margin width and ipsilateral breast tumor recurrence (IBTR) among 3,104 postmenopausal women with hormone receptor–positive DCIS enrolled in NSABP B-35. All patients underwent breast-conserving surgery followed by whole-breast irradiation (WBI) and received 5 years of endocrine therapy with either tamoxifen or anastrozole. (JAMA Network)

🔹 What did the study find?

Using a 1-mm threshold, the 10-year cumulative incidence of IBTR was:

• Margin <1 mm: 5.6%
• Margin ≥1 mm: 4.0%
• P = .04

Using a 2-mm threshold, the 10-year cumulative incidence was:

• Margin ≤2 mm: 5.3%
• Margin >2 mm: 3.8%
• P = .05

Although these differences were statistically significant or borderline significant on unadjusted analysis, the absolute differences were small—approximately 1.5–1.6% at 10 years. (JAMA Network)

More importantly, after adjustment for patient and tumor characteristics, margin width was no longer a significant independent predictor of ipsilateral recurrence. For the 2-mm threshold, the adjusted HR was 1.33 (95% CI, 0.86–2.06). (JAMA Network)

🔹 Why is this important?

Current SSO-ASTRO-ASCO consensus guidance has established 2 mm as the standard adequate margin for DCIS treated with breast-conserving surgery and WBI. However, the guideline already emphasizes that a negative margin <2 mm does not automatically mandate additional surgery and that clinical judgment should guide re-excision decisions. (ASCO Publications)

The B-35 data strengthen that concept.

For an appropriately selected postmenopausal patient with HR-positive DCIS, a negative but close margin should not necessarily trigger an automatic return to the operating room when the patient will receive whole-breast radiation and endocrine therapy.

The decision should incorporate the entire clinical picture: extent of DCIS near the margin, residual calcifications, which margin is close, patient age and comorbidities, anticipated radiation and endocrine therapy, and the potential cosmetic and morbidity consequences of another operation. (ASCO Publications)

My takeaway:
The goal of DCIS surgery should remain oncologically sound excision, but margin width should be interpreted as part of the overall treatment strategy rather than as an isolated number.

A 2-mm margin remains an important benchmark, but these prospective trial data support a more individualized approach to re-excision—particularly when the margin is negative and effective adjuvant therapy is planned.

Importantly, these findings should not be generalized to all patients with DCIS. The B-35 population consisted specifically of postmenopausal women with HR-positive DCIS receiving both WBI and endocrine therapy. (JAMA Network)

References

1. Wapnir IL, Cecchini RS, Dignam JJ, et al. Lumpectomy Margins and Local Recurrence in DCIS: Results From the NRG Oncology/NSABP B-35 Randomized Clinical Trial. JAMA Surg. 2026;161(9):861-869. doi:10.1001/jamasurg.2026.2340. (JAMA Network)
2. Morrow M, Van Zee KJ, Solin LJ, et al. Society of Surgical Oncology–American Society for Radiation Oncology–American Society of Clinical Oncology Consensus Guideline on Margins for Breast-Conserving Surgery With Whole-Breast Irradiation in Ductal Carcinoma In Situ. J Clin Oncol. 2016;34(33):4040-4046. (ASCO Publications)
3. Morrow M, Abrahamse P, Hofer TP, et al. Lumpectomy Margins for Invasive Breast Cancer and Ductal Carcinoma in Situ: Current Guideline Recommendations, Their Implications, and Impact. J Clin Oncol. 2020. (ASCO Publications)

Read the JAMA Surgery article

#BreastCancer #DCIS #BreastSurgery #SurgicalOncology #BreastConservingSurgery #Lumpectomy #CancerSurgery #RadiationOncology #PrecisionMedicine #Oncology