When the researchers stratified the local recurrence rates by margin status, they saw that 5% of patients with margins of 1 mm or smaller had LRRs within 10 years, as did 3.6% of those with margins from 1.1 to 2.9 mm, compared with just 0.07% of those with disease-free margins (P less than .001). There was no difference in LRR between the two narrow-margin groups.
Among 546 patients with an intact contralateral breast, the 10-year rate of contralateral breast disease was 6.4%.
On univariate analysis, significant predictors of LRR included margin status (P = .002), multicentric disease (P = .005), and necrosis (P = .005). On multivariate analysis, however, only margin status remained significant, with an HR of 8.0 (P = .006).
Dr. FitzSullivan said that the low rate of LRR of DCIS treated with mastectomy and close surgical margins, compared with the rate of contralateral breast cancer, suggests that routine postmastectomy radiation therapy is not warranted, and should be reserved only for those patients with close or positive surgical margins that cannot be surgically excised.
Each study was internally funded. Dr. Garvey and Dr. FitzSullivan reported having no financial disclosures.