BP5. Borderline epithelial lesions of the breast and low-grade DCIS show similar rates of subsequent ipsilateral DCIS and invasive disease: a 10-year follow-up report

Friday, March 6, 2026

8:30 AM - 8:37 AM MST

Location: 301A

Primary Presenter(s)

Claire M. Eden, MD

Department of Surgery
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Co-Author(s)

VS

Varadan Sevilimedu, MBBS, DrPH

Biostatistics Service, Department of Epidemiology and Biostatistics
Memorial Sloan Kettering Cancer Center
New York, New York, United States
Andrea V. Barrio, MD

Breast Service, Department of Surgery
Memorial Sloan Kettering Cancer Center
New York, New York, United States
Monica Morrow, MD (she/her/hers)

Chief, Breast Service, Department of Surgery; Anne Burnett Windfohr Chair of Clinical Oncology; Vice President, Women in Science and Medicine, MSKCC; Professor of Surgery, Weill Cornell Medical College of Cornell University
Memorial Sloan Kettering Cancer Center
New York, New York, United States
KV

Kimberly J. Van Zee, MD, MS

Breast Service, Department of Surgery
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Primary Author(s)

DC

Daniel Choi, MD

Breast Service, Department of Surgery
Memorial Sloan Kettering Cancer Center
New York, New York, United States

Introduction: Atypical ductal hyperplasia (ADH) and ductal carcinoma in-situ (DCIS) lie along a spectrum of ductal neoplasia. Histologic distinction between these entities can be challenging, with some ADH lesions described as bordering on DCIS, otherwise known as ‘borderline’ lesions (BLs). Risk of developing subsequent ipsilateral breast events (IBEs) after surgical excision of BLs remains unclear. This report provides long-term follow-up on IBEs for patients with BLs.

Methods: We queried a prospectively maintained database for patients undergoing breast-conserving surgery (+/- adjuvant endocrine or radiation therapy) for BL or DCIS between 1997 and 2016. We defined IBE as a subsequent diagnosis of DCIS or invasive cancer in the ipsilateral breast.

Results:

155 patients with BLs and 3544 patients with DCIS were identified with a median follow-up of 8.9 years. Compared to the DCIS cohort, the BL cohort was younger (p < 0.001), more often premenopausal (p < 0.001), less likely to undergo endocrine therapy (19% vs 28%, p = 0.012), and less likely to undergo radiation therapy (2% vs 60%, p < 0.001) (Table). 10-year IBE rates were 9.2% (95% CI 4.1-14.1%) for BL and 13.4% (95% CI 12.0-14.8%) for DCIS (p = 0.1). 10-year invasive-IBE rates were 6.0% (95% CI 2.8-11%) and 6.2% (95% CI 5.3-7.3%), respectively (p = 0.6).

Additional analyses were completed for patients with BL (n = 124), any-grade DCIS (n = 1073), and low-grade DCIS (n = 299), who did not receive adjuvant endocrine or radiation therapy. 10-year IBE rates were 10.7% for BL (95% CI 4.5-16.5%); 19.3% for any-grade DCIS (95% CI 16.4-22.1%)(BL vs. any-grade DCIS, p = 0.024); and 15.0% for low-grade DCIS (95% CI 10.0-19.8%)(BL vs. low-grade DCIS, p = 0.46). 10-year invasive-IBE rates were 6.6% for BL (95% CI 2.9-12%); 8.5% for any-grade DCIS (95% CI 6.6-11%) (p = 0.4); and 7.0% for low-grade DCIS (95% CI 4.0-11.0%) (p > 0.9).

Conclusions:

Compared to all DCIS, BLs had similar 10-year rates of IBEs and invasive IBEs. Without adjuvant therapies, any-grade DCIS patients were more likely to experience any IBE at 10 years but had similar 10-year invasive IBE rates. Without adjuvant therapies, BLs and low-grade DCIS had similar 10-year rates of any IBE and invasive IBE, suggesting that omission of adjuvant therapies should be considered for low-grade DCIS.

Learning Objectives:

After engaging with our presentation, participants should be able to understand the various diagnoses and treatments associated with ductal neoplasia.
After engaging with our presentation, participants should be able to understand rates of ipsilateral breast events and invasive events in patients with borderline epithelial lesions compared to patients with DCIS.
After engaging with our presentation, participants should be able to understand optimal adjuvant treatments for patients with borderline epithelial lesions and low-grade DCIS.