Background. The impact of close margins in patients with ductal carcinoma-in situ (DCIS) treated with mastectomy is unclear; however, this finding may lead to a recommendation for postmastectomy radiotherapy (PMRT). We sought to determine the incidence and consequences of close margins in patients with DCIS treated with mastectomy. Methods. The records of 810 patients with DCIS treated with mastectomy from 1996 through 2009 were reviewed. Clinical and pathologic factors were analyzed with respect to final margin status. Median follow-up was 6.3 years. Results. Overall, 94 patients (11.7 %) had close margins (positive, n = 5; negative but B1 mm, n = 54; 1.1-2.9 mm, n = 35). Independent risk factors for close margins included multicentricity, pathologic lesion size C1.5 cm, and necrosis, but not age, use of skin-sparing mastectomy, or immediate reconstruction (p[0.05). Seven patients received PMRT, and none had a locoregional recurrence (LRR). Among the remaining 803 patients, the 10-year LRR rate was 1 %(5.0 % for margins B1 mm, 3.6 %for margins 1.1-2.9 mm, and 0.7 % for margins C3 mm [p\0.001]).
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