Timing of Chemotherapy After MammoSite Radiation Therapy System Breast Brachytherapy: Analysis of the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial

Purpose: To evaluate cosmetic outcome and radiation recall in the American Society of Breast Surgeons registry trial, as a function of the interval between accelerated partial breast irradiation (APBI) and initiation of chemotherapy (CTX). Methods and Materials: A total of 1440 patients at 97 institutions participated in this trial. After lumpectomy for early-stage breast cancer, patients received APBI (34 Gy in 10 fractions) with MammoSite RTS brachytherapy. A total of 148 patients received CTX within 90 days of APBI. Cosmetic outcome was evaluated at each follow-up visit and dichotomized as excellent/good or fair/poor. Results: Chemotherapy was initiated at a mean of 3.9 weeks after the final MammoSite procedure and was administered ≤3 weeks after APBI in 54 patients (36%) and >3 weeks after APBI in 94 patients (64%). The early and delayed groups were well balanced with respect to multiple factors that may impact on cosmetic outcome. There was a superior cosmetic outcome in those receiving chemotherapy >3 weeks after APBI (excellent/good in 72.2% at ≤3 weeks vs. excellent/good in 93.8% at >3 weeks; p = 0.01). Radiation recall in those receiving CTX at ≤3 weeks was 9 of 50 (18%), compared with 6 of 81(7.4%) in those receiving chemotherapy at >3 weeks (p = 0.09). Conclusion: The majority of patients receiving CTX after APBI have excellent/good cosmetic outcomes, with a low rate of radiation recall. Chemotherapy initiated >3 weeks after the final MammoSite procedure seems to be associated with a better cosmetic outcome and lower rate of radiation recall. An excellent/good cosmetic outcome in patients receiving CTX after 3 weeks was similar to the cosmetic outcome of the overall patient population who did not receive CTX.