Tumor bed control with balloon-based accelerated partial breast irradiation: incidence of true recurrences versus elsewhere failures in the American Society of Breast Surgery MammoSite(®) Registry Trial.

Background: Randomized trials demonstrate that lumpectomy plus whole-breast irradiation (WBI) yields survival equivalent to mastectomy. Studies that use WBI, however, typically report higher tumor bed recurrence rates than elsewhere failures (EF) (historically considered new primary lesions). The rate of true recurrence (TR) versus EF was queried for a large patient cohort treated with accelerated partial breast irradiation (APBI).
Methods: A total of 1,449 cases of early-stage breast cancer were treated on the American Society of Breast Surgeons MammoSite(®) Registry Trial with lumpectomy plus balloon-based APBI (34 Gy, 10 BID fractions). A total of 1,255 cases (87 %) had invasive breast cancer, and 194 patients (13 %) had ductal carcinoma in situ. Rates of TR versus EF were calculated and compared to historical WBI controls.
Results: Median follow-up was 60 (range 0-109) months. Fifty patients (3.5 %) developed an ipsilateral breast tumor recurrence (IBTR). The 5-year actuarial rate of IBTR was 3.6 % (invasive breast cancer 3.6 %, ductal carcinoma in situ 3.4 %). Fourteen IBTR (1.1 %) were TR, while 36 (2.6 %) were EF. Estrogen receptor-negative status was associated with IBTR for invasive malignancies as well as for EF only (p < 0.001). Trends for increased rates of EF were noted for increased tumor size (p = 0.067) and extensive intraductal component (p = 0.087). No pathologic factors were explicitly associated with TR.
Conclusions: IBTR after balloon-based APBI is low and similar to rates reported for WBI. In this data set, APBI had fewer tumor bed recurrences (presumably initial cancer recurrences) than EF (presumably new primary lesions). This suggests that balloon-based APBI has a tumor bed control rate that is at least equal to (and potentially higher than) WBI.