Close or positive margins after mastectomy for DCIS: pattern of relapse and potential indications for radiotherapy.

Purpose: Mastectomies result in very high local control rates for pure ductal carcinoma in situ; however, close or involved tumor margins are occasionally encountered. Data regarding the patterns of relapse in this setting are limited.
Methods and Materials: Between 1994 and 2002, the pathology reports of 574 patients who had undergone mastectomy at our institution for pure ductal carcinoma in situ were retrospectively reviewed. Of the 574 patients, 84 were found to have margins of <10 mm. Of the 84 patients, 4 underwent postoperative radiotherapy and were excluded, leaving 80 patients for this analysis. Of the 80 patients, 31 had margins <2 mm and 49 had margins of 2.1-10 mm. High-grade disease was observed in 47 patients; 45 patients had comedonecrosis; and 30 had multifocal disease. Of the 80 patients, 51 were <60 years of age.
Results: With a median follow-up of 61 months, 6 (7.5%) of the 80 patients developed local recurrence. Of the 31 patients with a margin of <or=2 mm, 5 (16%) developed local recurrence vs. only 1 (2%) of 49 patients with a margin of 2.1-10 mm (p = 0.0356). Of the 6 patients with local recurrence, 5 had high-grade disease and/or comedonecrosis. All six recurrences were noted in patients <60 years old.
Conclusion: The findings of this review suggest that patients with pure ductal carcinoma in situ who undergo mastectomy with a margin of <2 mm have a greater-than-expected incidence of local recurrence. Patients with additional unfavorable features such as high-grade disease, comedonecrosis, and age <60 years are particularly at risk of local recurrence. These patients might benefit from postmastectomy radiotherapy.