Effectiveness and toxicity of re-irradiation after breast conserving surgery for recurrent or new primary breast cancer: a multi-institutional study

Abstract Purpose: Breast reirradiation (reRT) after breast conserving surgery (BCS) has emerged as a viable alternative to mastectomy for women presenting with recurrent or new primary breast cancer. There are limited data on safety of different fractionation regimens. This multi-institutional study reports safety and efficacy among women treated with repeat BCS and reRT. Methods and Materials: Patients who underwent repeat BCS followed by RT from 2015–2021 at 2 institutions were analyzed. Univariate logistic regression models were used to identify predictors of acute and late toxicities. Kaplan Meier estimates were used to evaluate overall survival (OS), distant metastasis free survival (DMFS) and locoregional recurrence-free survival (LR-RFS). Results: Sixty-six patients were reviewed with median follow-up of 16 months (range: 3–60 months). At time of first recurrence, 41% had invasive carcinoma with a ductal carcinoma in situ (DCIS) component, 41% had invasive carcinoma alone and 18% had DCIS alone. All were clinically node negative. For the reirradiation course, 95% received partial breast irradiation (PBI) (57.5% with 1.5Gy BID; 27% with 1.8Gy daily; 10.5% with hypofractionation), and 5% received whole breast irradiation (1.8-2Gy/fx), all of whom had received PBI for initial course. One patient experienced grade 3 fibrosis, and one patient experienced grade 3 telangiectasia. None had grade 4 or higher late adverse events. We found no association between the fractionation of the second course of RT or the cumulative dose (measured as EQD2) with acute or late toxicity. At 2 years, OS was 100%, DMFS was 91.6%, and LR-RFS was 100%. Conclusion: In this multi-institutional series of patients with recurrent or new primary breast cancer, a second breast conservation surgery followed by reirradiation was effective with no local recurrences and an acceptable toxicity profile across a range of available fractionation regimens.