Efficacy and safety of post-mastectomy radiation therapy for patients with breast cancer after breast reconstruction: A retrospective multicenter cohort study (Reborn-03).

Abstract

579 Background: A cornerstone of multidisciplinary treatment for breast cancer, breast reconstruction has recently been extended to high-risk patients with breast cancer who require post-mastectomy radiation therapy (PMRT). PMRT reduces the 10-year risk of locoregional recurrence; however, its association with postoperative complications remains unclear. This study aimed to evaluate the efficacy and safety of PMRT in patients with high-risk breast cancer who underwent breast reconstruction. Methods: This retrospective cohort study included patients with high-risk breast cancer who underwent immediate or delayed breast reconstruction after mastectomy between 2008 and 2018. High-risk patients were defined as those with positive axillary lymph nodes, clinical tumor size of >5 cm, chest wall invasion, or skin invasion. Patient data were collected from participating institutions and analyzed retrospectively. Results: Of the 1,138 patients, 427 (37.5%) underwent PMRT and 711 (62.5%) did not. The median age at surgery was 46 years (range, 23–76years), and the median follow-up period was 8 years. The number of patients meeting more than two high-risk criteria was 149 (23.9%) and 81 (11.4%) in the PMRT and non-PMRT cohorts, respectively. Breast reconstruction using silicone breast implants (SBI) was performed in 70% and 71.4% of patients in the PMRT and non-PMRT cohorts, respectively. The locoregional recurrence rates were 7.7% and 12.7% in the PMRT and non-PMRT cohorts, respectively (P=0.034). Multivariate analysis revealed that PMRT was an independent predictive factor for reducing locoregional recurrence (P<0.001) (Table 1). Complications occurred in 130 patients (30.4%) in the PMRT cohort and 168 (23.6%) in the non-PMRT cohort (P=0.016). The reoperation rates due to complications were 46 (35.4%) in the PMRT cohort and 61 (36.3%) in the non-PMRT cohort (P = 0.100). In the PMRT cohort, 62 patients (14.5%) experienced grade 2 radiation-induced dermatitis, and three patients (0.7%) developed grade 2 radiation-induced pneumonia. Conclusions: Although the incidence of adverse events was slightly higher in the PMRT cohort, the reoperation rates due to complications were comparable between the cohorts. PMRT is a safe and effective modality that provides substantial benefits for locoregional recurrence reduction in patients with high-risk breast cancer undergoing breast reconstruction. Multivariate analysis for locoregional recurrence in patients with high-risk breast cancer who underwent breast reconstruction. Factors Hazard ratio 95% Confidence interval P-value PMRT 0.40 0.251-0.623 <0.001 Neoadjuvant therapy 3.43 2.29-5.12 <0.001 pT (>5 cm) 1.95 1.25-3.03 0.003 Surgical margin 1.96 1.01-3.81 0.047