Morrow, MonicaVan Zee, Kimberly J.Solin, Lawrence J.Houssami, NehmatChavez-MacGregor, MarianaHarris, JayHorton, JanetHwang, ShelleyJohnson, Peggy L.Marinovich, M. LukeSchnitt, StuartWapnir, IreneMoran, Meena S.2017-07-242016Morrow, M., K. J. Van Zee, L. J. Solin, N. Houssami, M. Chavez-MacGregor, J. R. Harris, J. Horton, et al. 2016. “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.” Journal of Clinical Oncology 34 (33): 4040-4046. doi:10.1200/JCO.2016.68.3573. http://dx.doi.org/10.1200/JCO.2016.68.3573.http://nrs.harvard.edu/urn-3:HUL.InstRepos:33490751Background: Controversy exists regarding the optimal negative margin width for ductal carcinoma in situ (DCIS) treated with breast-conserving surgery and whole-breast irradiation (WBRT). Methods: A multidisciplinary consensus panel used a meta-analysis of margin width and ipsilateral breast tumor recurrence (IBTR) from a systematic review of 20 studies including 7883 patients and other published literature as the evidence base for consensus. Results: Negative margins halve the risk of IBTR compared with positive margins defined as ink on DCIS. A 2 mm margin minimizes the risk of IBTR compared with smaller negative margins. More widely clear margins do not significantly decrease IBTR compared with 2 mm margins. Negative margins less than 2 mm alone are not an indication for mastectomy, and factors known to impact rates of IBTR should be considered in determining the need for re-excision. Conclusion: The use of a 2 mm margin as the standard for an adequate margin in DCIS treated with WBRT is associated with low rates of IBTR and has the potential to decrease re-excision rates, improve cosmetic outcome, and decrease health care costs. Clinical judgment should be used in determining the need for further surgery in patients with negative margins < 2 mm.en-USSurgeryASCO GuidelinesJournal Article2017-07-2410.1200/JCO.2016.68.3573