D. Schreiber1, Y. Cotterell2, M. Karp3, A. T. Wong1, S. Sharma1, D. Addis1, W. Polen1, P. Jadeja1, A. Price1, S. Fuzesi1, and W. Diehl1; 1Summit Health, Berkeley Heights, NJ, 2SUNY Downstate Medical Center, Brooklyn, NY, 3Department of Radiation Oncology, State University of New York (SUNY) Downstate Medical Sciences University and Maimonides Medical Center, Brooklyn, NY
Purpose/Objective(s): Multiple reports, as well as ongoing prospective trials are evaluating or have already suggested that radiation can be eliminated for women with low risk, ER+ breast malignancies, due to equivalent survival with endocrine therapy alone. However, given the low toxicity of partial breast irradiation (PBI), shorter duration of modern therapies, and historically poor compliance rates with endocrine therapy, partial breast radiation is an excellent alternative option, with completion of therapy in 1-3 weeks. In this retrospective study, we sought to evaluate tolerance, toxicity and outcomes in women who elected partial breast radiation in a large community based practice. Materials/
Methods: All women ages 40 or older treated with partial breast radiation at our institution from 2018-2021 were included. All patients underwent lumpectomy with negative margins. All histologies were allowed, including invasive lobular carcinoma as well as ductal carcinoma in situ. Details regarding tolerance to radiation, endocrine therapy, side effects, local, regional, and distant control were recorded. Kaplan Meier analysis was used to analyze the local, regional, and distant control endpoints. Results: There were 135 patients included. The median age was 64 (interquartile range 56-71). Most patients (67.4%) had invasive ductal histology, ductal carcinoma in situ (22.2%), or invasive lobular carcinoma/mixed ductal/lobular carcinoma (9.6%). Median follow up was 36 months (Interquartile range 29-52). Endocrine therapy was started in 117 patients (86.7%) and of those, 26 (22%) stopped early due to side effects. All patients completed radiation without treatment related delays. The most common radiation techniques included 40Gy/15 fractions (n=109) and 26.2-30Gy/5 fractions (n=22 ). Short term grade 2 side effects included breast pain/dry desquamation in 5.1% of patients. Long term grade 2 side effects included breast fibrosis/pain in 2 patients (1.4%). Both of these were in the 5 fraction regimen. There were no long term grade 2+ side effects in the 15 fraction patients. There were no local breast recurrences and the 3 year local control rate was 100%. There was one patient with a regional and distant recurrence at 34 months for a 3 year regional and distant control rate of 98.6% . Conclusion: Partial breast radiation was very well tolerated in this community setting, with excellent local control outcomes and minimal grade 2 toxicity. Endocrine therapy had a high compliance overall, but still had a 22% early termination rate. Given the excellent control and low toxicity outcomes with minimal morbidity, partial breast radiation should continue to be explored in these settings as a viable alternative to radiation omission.
