Reirradiation of Breast Cancer In-Field Recurrences with Curative Intent: Locoregional Practice Patterns, Toxicity, and Survival Outcomes

The growing number of breast cancer survivors is expected to increase the absolute number of locoregional recurrences requiring management, necessitating improvements in treating recurrences or tumours that occur within the initial radiation field (IFR). However, there are no guidelines on reirradiation (RT2) for breast cancer IFRs. We aimed to investigate locoregional practice patterns and outcomes. We retrospectively identified patients who received adjuvant RT1 for resected breast cancer and subsequently received curative-intent RT2 for IFRs at two large tertiary centres. A chart review obtained treatment, patient, and tumour characteristics. Descriptive statistics were calculated to characterize practice patterns, toxicity, and survival outcomes. Thirty-five patients met inclusion criteria across 18 years, with mean follow-up time of 43 months. Median time from RT1 to progression was 70.1 months. Most IFRs were in the breast or chest wall alone (48.6%). Regional nodal irradiation (RNI) was given in 23% of RT1 and 48.6% of RT2. Complete field overlap occurred in 60% of patients. Ten patients (28.6%) had a second recurrence (i.e., after RT2). Five-year OS was 65.4%, the median OS was not reached, and the mean OS was 73.7 months (95% CI 59.8–87.7 months). Freedom from recurrence (after RT2) was 71%. Shorter time to initial recurrence was associated with second recurrence (p = 0.018), and second recurrence was found to be predictive of death (p < 0.001). Four (11.4%) patients developed fibrosis, 75% of which developed after RT1. Eight (22.9%) patients developed lymphedema, 75% of which developed after RT1, all of which were documented as stable after RT2. Managing breast cancer IFRs with RT2 appears to be a feasible approach with reasonably consistent practice patterns in appropriately selected patients. Toxicity appears to be driven by the initial treatment course, and survival outcomes are acceptable.