The influence of margin width on local control of ductal carcinoma in situ of the breast.

BACKGROUND Ductal carcinoma in situ is a non-invasive carcinoma that is unlikely to recur if completely excised. Margin width, the distance between the boundary of the lesion and the edge of the excised specimen, may be an important determinant of local recurrence. METHODS Margin widths, determined by direct measurement or ocular micrometry, and standardized evaluation of the tumor for nuclear grade, comedonecrosis, and size were performed on 469 specimens of ductal carcinoma in situ from patients who had been treated with breast-conserving surgery with or without postoperative radiation therapy, according to the choice of the patient or her physician. We analyzed the results in relation to margin width and whether the patient received postoperative radiation therapy. RESULTS The mean (+/-SE) estimated probability of recurrence at eight years was 0.04+/-0.02 among 133 patients whose excised lesions had margin widths of 10 mm or more in every direction. Among these patients there was no benefit from postoperative radiation therapy. There was also no statistically significant benefit from postoperative radiation therapy among patients with margin widths of 1 to <10 mm. In contrast, there was a statistically significant benefit from radiation among patients in whom margin widths were less than 1 mm. CONCLUSIONS Postoperative radiation therapy did not lower the recurrence rate among patients with ductal carcinoma in situ that was excised with margins of 10 mm or more. Patients in whom the margin width is less than 1 mm can benefit from postoperative radiation therapy.