Three-year analysis of treatment efficacy, cosmesis, and toxicity by the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial in patients treated with accelerated partial breast irradiation (APBI)

BACKGROUND. This report presents 3 years of data on treatment efficacy, cosmetic results, and toxicities for patients enrolled on the American Society of Breast Surgeons MammoSite (Cytyc, Bedford, Mass) Breast Brachytherapy Registry Trial. METHODS. A total of 1440 patients (1449 cases) with early stage breast cancer who were undergoing breast-conserving therapy were treated with the MammoSite device to deliver accelerated partial breast irradiation (APBI) (34 Gy in 3.4 Gy fractions). Of these, 1255 (87%) cases had invasive breast cancer (IBC; median size = 10 mm), and 194 (13%) cases had ductal carcinoma in situ (DCIS; median size = 8 mm). Median follow-up was 30.1 months. RESULTS. Twenty-three (1.6%) cases developed an ipsilateral breast tumor recurrence (IBTR) for a 2-year actuarial rate of 1.04% (1.11% for IBC and 0.59% for DCIS). No variables were associated with IBTR. Six (0.4%) patients developed an axillary failure. The percentages of breasts with good to excellent cosmetic results at 12 (n = 980), 24 (n = 752), 36 (n = 403), and 48 months (n = 67 cases) were 95%, 94%, 93%, and 93%, respectively. Breast seromas were reported in 23.9% of cases (30% in open-cavity implants and 19% in closed-cavity implants). Symptomatic seromas occurred in 10.6% of cases, and 1.5% of cases developed fat necrosis. A subset analysis of the first 400 consecutive cases enrolled was performed (352 with IBC, 48 DCIS). With a median follow-up of 37.5 months, the 3-year actuarial rate of IBTR was 1.79%. CONCLUSIONS. Treatment efficacy, cosmesis, and toxicity 3 years after treatment with APBI using the MammoSite device are good and similar to those reported with other forms of APBI with similar follow-up.