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

Abstract

529 Background: This report presents 2-year data on treatment efficacy and cosmesis for patients enrolled on the ASBS sponsored MammoSite Registry trial. Methods: 1449 patients were treated with the MammoSite device to deliver APBI. 924 patients have been followed ≥ 12 months, 586 ≥ 18 months, 316 ≥ 24 months and 52 ≥ 36 months. Median follow-up for surviving patients was 14 months. Results: Eleven patients (0.8%) developed an ipsilateral breast tumor recurrence (IBTR) as some component of their initial failure (prior to distant metastases [DM]) for a 2-yr actuarial rate of 1.2%. The 2-yr actuarial rate of isolated IBTR was 0.8% (n=8). Six patients (0.4%) developed an axillary failure (AF) as some component of their initial failure (prior to DM) for a 2-yr actuarial rate of 1.0%. The 2-yr actuarial rate of isolated AF was 0.6% (n=3). The only variable associated with the development of an isolated IBTR (n=8) included an extensive intraductal component (p=0.073) (patient age, margin status, grade, histology, tumor size, nodal status, use of systemic therapy and method of device placement were not associated with IBTR). The only variable associated with the development of all IBTRs (n=11) was tumor location (inner quadrant, p=0.079). The percentage of patients with good/excellent cosmetic results at 6, 12, 18, 24 and 36 months were as follows: 95.1% (n=769 patients), 93.7% (n=621 patients), 91.3% (n=344 patients), 93.5% (n=248 patients), and 90.4% (n=52 patients) (p=NS). For the 174 patients with both a 12-month and 24 month cosmetic assessment, the rate of good/excellent cosmetic results was 94% at 12 and 24 months. At 24 months (n=248 patients), factors associated with good/excellent cosmetic results included increased skin spacing as a categorical variable (94.8% versus 86.1%, p=0.064), no infection (94.8% versus 85.7%, p=0.057), and no systemic chemotherapy treatment (95.3% versus 82.4%, p=0.012). Conclusions: Treatment efficacy and cosmesis 2 years after treatment with APBI using the MammoSite device are excellent and appear similar to those reported with standard whole breast RT. No significant financial relationships to disclose.