American Society of Breast Surgeons MammoSite Radiation Therapy System Registry Trial: ductal carcinoma-in-situ subset analysis-4-year data in 194 treated lesions

Background: A subset analysis of the American Society of Breast Surgeons (ASBS) Registry Trial of patients with ductal carcinoma-in-situ (DCIS) was performed to compare results to patients receiving accelerated partial breast irradiation (APBI) for invasive tumors and to results in patients with DCIS receiving whole breast irradiation. Methods: One hundred ninety-four cases of DCIS were identified from a total of 1,449 cancers treated on the ASBS Registry Trial. Details of the trial are previously published. Analysis of the entire group of cases was performed in regards to toxicity and local control. Results: Median age was 62.1 years with 40.1% and 10.9% younger than 60 years and 50 years, respectively. Nuclear grade distribution was 35.6%, 31.4%, 17%, and 16% high, intermediate, low grade, and unknown, respectively. Necrosis was known to be present 42.3% of cases. Comedo/solid architecture was known to be present in 68% of cases. Median tumor size was 8.0 mm (range .1-45 mm, 15.5% unknown). Median margin was 2 mm; 2 cases had positive margins and 56 cases had less than 1-mm margins. The median follow-up time was 46.7 months. Five isolated ipsilateral breast failures occurred. The actuarial isolated ipsilateral breast failure rate was 2.45% at 4 years. The total in-breast 4-year actuarial failure rate was 3.0%. Three of the patients had a failure elsewhere (1.69% 4-year actuarial rate). Three of the failures were true recurrences (1.33% 4-year actuarial rate). Infection occurred in 16 patients for an 8.2% rate. Seroma formation was reported in 31%, with 13% and 12% symptomatic and requiring intervention, respectively. Seroma formation was statistically higher in open versus closed cases for all seromas. Cosmetic outcome was good to excellent in 90.3% of patients with evaluation at 36 months. Conclusions: The ASBS Registry Trial includes the largest published collection of DCIS treated with APBI. Four-year follow-up shows result similar to those with invasive cancer treated with APBI, as well as DCIS treated with whole breast irradiation.