Impact of margin status on outcomes following accelerated partial breast irradiation using single-lumen balloon-based brachytherapy

PURPOSE: To examine the impact of margin status on clinical outcomes for patients enrolled in the American Society of Breast Surgeons (ASBrS) MammoSite (R) Registry Trial: METHODS AND MATERIALS: One thousand four hundred forty-nine cases of early-stage breast cancer underwent breast-conserving therapy with a single-lumen balloon-based applicator used to deliver adjuvant accelerated partial breast irradiation (34 Gy in 10, bid fractions). One thousand two hundred fifty-five cases (87%) had invasive breast cancer (median size = 10 mm) and 194 cases (13%) had ductal carcinoma in situ (DCIS; median size = 8 mm). RESULTS: Patients were stratified by margin status into negative (n = 1326), close (<2mm; 72 = 110), and positive (n = 13) margins. One hundred twenty-three cases (8.5%) had close or positive margins. Overall, no statistical difference in the 6-year rate of ipsilateral breast tumor recurrence (IBTR) was noted for close margins compared with that of margin-negative patients (8.7% vs. 4.1%, p = 0.10) or for positive margins compared with that of margin-negative patients (14.3% vs. 4.1%, p = 0.41). In patients with DCIS, there was a statistically significant increase in IBTR with close margins (17.6% vs. 4.2%, p = 0.004) and when close and positive margins were pooled (15.7% vs. 4.2%, p = 0.01 with a nonsignificant reduction in disease-free survival for DCIS patients with close margins (82.4% vs. 90.8%, p = 0.12). The increase in IBTR for close and close/positive patients was secondary to statistically significant increases in elsewhere failures rather than true recurrences/marginal misses. CONCLUSION: Nonsignificant increases in the rates of IBTR were noted with close and positive margins for invasive cancer with further data required to validate these findings. 2013 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.