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

To examine the impact of margin status on clinical outcomes for patients enrolled in the American Society of Breast Surgeons (ASBrS) MammoSite(®) Registry Trial.

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 (34Gy in 10, bid fractions). One thousand two hundred fifty-five cases (87%) had invasive breast cancer (median size=10mm) and 194 cases (13%) had ductal carcinoma in situ (DCIS; median size=8mm).

Patients were stratified by margin status into negative (n=1326), close (<2mm; n=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.

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.