Three national cancer organizations have come together to issue a consensus guideline intended to provide clarity regarding the optimal negative margin width for treating women diagnosed with ductal carcinoma in situ (DCIS) who have undergone breast-conserving surgery and whole-breast irradiation (WBRT). The Society of Surgical Oncology, the American Society for Radiation Oncology, and the American Society of Clinical Oncology published the new guideline in their respective journals, the Annals of Surgical Oncology, Practical Radiation Oncology, and the Journal of Clinical Oncology.1 To create the new guideline, the Society of Surgical Oncology put together a multidisciplinary panel of experts that included clinicians and researchers from all three organizations in addition to a patient advocate. The group 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 basis for the consensus. The guideline authors say that retrospective single-institution studies have suggested that a negative margin width of 1 cm or more may eliminate the reduction in IBTR seen in patients undergoing WBRT. Furthermore, despite the widespread use of breast-conserving therapy (BCT) for DCIS, the panel says that there was no previous consensus on what constitutes an optimal negative margin width. Thus, approximately 1 in 3 women attempting BCT for DCIS undergo re-excision. It was this lack of consensus that lead the panel to convene. The panel concluded that the use of a 2-mm margin as the standard in women diagnosed with DCIS and treated with WBRT is associated with low rates of IBTR and has the potential to decrease re-excision rates, improve cosmetic outcome, and decrease the cost of care. They also concluded that margins wider than 2 mm do not significantly reduce the rates of recurrence when compared with 2-mm margins, and their routine use is not supported by the evidence. See “Summary of Key Recommendations from the New DCIS Consensus Guideline,” left, for the main points of the panel's recommendations. Bruce G. Haffty, MD, immediate past chair of the American Society for Radiation Oncology board of directors, said that the new guideline will assist clinicians who have struggled with margin width in this patient population. “While the guideline appropriately allows for some flexibility and clinical judgment in interpretation,” he says, “the conclusion that a 2-mm margin width is adequate in patients with DCIS will be helpful and reassuring to clinicians and patients in clinical decision making.” There are some limitations to the guideline: It applies only to patients who have been diagnosed with DCIS and DCIS with microinvasion and treated with WBRT, and the findings should not be applied to patients with DCIS treated with accelerated partial-breast irradiation or to those who have invasive carcinoma.