For postmenopausal women with hormone receptor–positive ductal carcinoma in situ (DCIS) treated with breast-conserving surgery, whole-breast irradiation, and adjuvant endocrine therapy, reexcision to achieve wider surgical margins (≥ 1 mm or ≥ 2 mm) may not be necessary, according to data presented at the 2025 American Society of Breast Surgeons (ASBrS) Annual Meeting.¹ Analysis of the large NRG Oncology/NSABP B-35 trial found that differences in 10-year ipsilateral breast tumor recurrence rates were small and potentially not clinically meaningful when comparing those who had narrow margins (< 1 mm or < 2 mm) with those who had wider margins (≥ 1 mm or ≥ 2 mm) within specific patient cohorts.

“The current recommendation for patients with DCIS undergoing lumpectomy is a 2-mm disease-free margin, and if margins are found to be ≤ 2 mm, women often return to the operating room to remove additional tissue,” said lead study author Irene L. Wapnir, MD, a surgical oncologist and Professor of Surgery at Stanford Medicine. “This study is extremely important because it suggests reexamination of the need for reexcision.”

As Dr. Wapnir explained, ductal carcinoma in situ is the earliest type of breast cancer, confined to the milk ducts. Standard treatment often involves breast-conserving surgery (lumpectomy) followed by whole-breast irradiation. For hormone receptor–positive ductal carcinoma in situ, adjuvant endocrine therapy is also commonly prescribed.

Surgical margins less than the recommended 2 mm or greater threshold frequently lead to recommendations for reexcision surgery to reduce the risk of local recurrence. However, noted Dr. Wapnir, reoperations carry potential downsides, including increased patient anxiety, poorer cosmetic outcomes from larger tissue removal, and additional health-care costs and use of resources.

Study Methods

The NSABP B-35 trial was a double-blind study that enrolled 3,104 postmenopausal women with hormone receptor–positive ductal carcinoma in situ between 2003 and 2006. Patients were randomly assigned to receive either tamoxifen or anastrozole for 5 years, in addition to undergoing lumpectomy and whole-breast irradiation. Because the local recurrence rates between the two endocrine therapy arms were similar and not statistically different, the trial provided a robust data set to analyze the impact of other factors, such as margin width, on local tumor control. Margin data were prospectively collected by participating pathologists.

Researchers analyzed two subgroups based on the available margin information. In the first group of 2,707 patients, margins were classified as either < 1 mm (close/indefinite) or 1 mm or greater (negative). In the second group of 2,546 patients, the specific measurement of the closest margin was available, allowing analysis of the use of a 2-mm cutoff (< 2 mm vs ≥ 2 mm).

Ipsilateral Breast Tumor Recurrence Rates

The primary endpoint of interest was the cumulative incidence of ipsilateral breast tumor recurrence. In the analysis using the 1-mm cutoff, the 10-year rate was 5.6% for patients with margins < 1 mm (n = 502) vs 4.0% for those with margins ≥ 1 mm (n = 2,205). Although a statistically significant difference existed, the absolute difference was only 1.6% at 10 years, said Dr. Wapnir.

Similarly, using the 2-mm cutoff, the 10-year cumulative incidence rate of ipsilateral breast tumor recurrence was 5.3% for patients with margins < 2 mm (n = 879) vs 3.8% for those with margins ≥ 2 mm (n = 1,667). This represented an absolute difference of 1.5%. Analyses of all breast cancer events (including contralateral cancers) did not show statistically significant differences based on margin width at either cutoff.

“The differences in the rates of ipsilateral breast tumor recurrence using a 1- or 2-mm cutoff margin width were small and we believe not clinically meaningful,” said Dr. Wapnir. “These findings suggest that, within the context of this specific patient population receiving lumpectomy, whole-breast irradiation, and 5 years of adjuvant endocrine therapy, the modest reduction in ipsilateral breast tumor recurrence associated with achieving wider margins (≥ 1 mm or ≥ 2 mm) compared with narrower margins may not justify the routine practice of reexcision.” The authors emphasized that these results apply specifically to postmenopausal women with estrogen receptor–positive and progesterone receptor–positive ductal carcinoma in situ treated with this comprehensive approach.

“The study provides important data to support reevaluation of margin width guidelines for this patient subgroup, potentially leading to less frequent reoperations and improved patient experience without compromising long-term local control outcomes,” Dr. Wapnir concluded.

Expert Point of View

Chandler S. Cortina, MD, MS, FSSO, FACS, Associate Professor of Surgery at Medical College of Wisconsin, said that the results of the prospective NSABP B-35 trial suggest that wider ductal carcinoma in situ (DCIS) lumpectomy margins may not provide a clinically meaningful reduction in local recurrence for postmenopausal women with hormone receptor–positive ductal carcinoma in situ.

“At 10 years, the absolute difference in recurrence was only 1.6% using a 1-mm margin cutoff and only 1.5% with a 2-mm cutoff,” Dr. Cortina told The ASCO Post. “These findings indicate that margin reexcision may be unnecessary for select patients with margins ≤ 2 mm and inform shared decision-making between patients and the multidisciplinary team.”

Of note, Dr. Cortina added, all women in this clinical trial also received adjuvant whole-breast irradiation, with an optional boost, and 5 years of endocrine therapy. In real-world settings, not all patients who undergo lumpectomy for ductal carcinoma in situ will receive dual adjuvant therapy because of contraindications, side effects, or comorbidities.

“Therefore, these results should not be generalized to premenopausal patients, those with hormone receptor–negative DCIS, or those who aren’t able to receive standard adjuvant therapy,” Dr. Cortina concluded. “Nevertheless, the findings prompt the question that we may need to reassess how we define optimal margin width for postmenopausal women who undergo lumpectomy for hormone receptor–positive DCIS, with the goal of reducing unnecessary surgery.”

DISCLOSURE: Dr. Wapnir reported no conflicts of interest. Dr. Cortina reported no conflicts of interest.

REFERENCE

1. Wapnir IL, Cecchini R, Dignam J, et al: Margin width and local recurrence in the NRG Oncology/NSABP B-35 DCIS Lumpectomy Trial. 2025 ASBrS Annual Meeting. Abstract 1985885. Presented May 2, 2025.