Treatment Efficacy with Accelerated Partial Breast Irradiation (APBI): Final Analysis of the American Society of Breast Surgeons MammoSiteA® Breast Brachytherapy Registry Trial

The purpose of this study was to examine data on treatment efficacy, cosmesis and toxicities for the final analysis of the American Society of Breast Surgeons MammoSite(A (R)) breast brachytherapy registry trial. A total of 1,449 cases of early-stage breast cancer underwent breast conserving therapy. The single-lumen MammoSite(A (R)) device was used to deliver accelerated partial breast irradiation (APBI) (34 Gy in 3.4 Gy fractions). Of these, 1,255 cases (87 %) had invasive breast cancer (IBC) and 194 cases had DCIS. Median follow-up was 63.1 months with 45 % of all patients having follow-up of 6 years or longer. There were 41 cases (2.8 %) that developed an ipsilateral breast tumor recurrence (IBTR) for a 5-year actuarial rate of 3.8 % (3.7 % for IBC and 4.1 % for DCIS). Tumor size (odds ratio [OR] = 1.1, p = 0.03) and estrogen receptor negativity (OR = 3.0, p = 0.0009) were associated with IBTR, while a trend was noted for positive margins (OR = 2.0, p = 0.06) and cautionary/unsuitable status compared with suitable status (OR = 1.8, p = 0.07). The percentage of patients with excellent/good cosmetic results at 60, 72, and 84 months was 91.3, 90.5, and 90.6 %, respectively. The overall rates of fat necrosis and infections remained low at 2.5 and 9.6 % with few late toxicity events beyond 2 years. The overall symptomatic seroma rate was 13.4 and 0.6 % beyond 2 years. The final analysis of treatment efficacy, cosmesis, and toxicity from the American Society of Breast Surgeons MammoSite(A (R)) breast brachytherapy registry trial confirms previously noted excellent results and compares favorably with other forms of APBI with similar follow-up and to outcomes seen in selected patients treated with whole breast irradiation.