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

[INTRODUCTION] Post-mastectomy radiation therapy (PMRT) is a standard treatment modality for patients with high-risk breast cancer. Although it is performed in patients who undergo breast reconstruction (BR), PMRT efficacy following BR in patients with high-risk breast cancer remains unclear. We evaluated the effectiveness of PMRT in patients with high-risk breast cancer who underwent BR.

[MATERIALS AND METHODS] This 15-institution retrospective cohort study included patients with high-risk breast cancer who underwent immediate or delayed BR 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.

[RESULTS] Of the 1138 included patients, 427 (37.5 %) received PMRT, whereas 711 (62.5 %) did not. The median age at surgery was 46 (range 23-76) years, and the median follow-up period was 8 years. Overall, 149 (34.9 %) and 81 (11.4 %) patients in the PMRT and non-PMRT cohorts, respectively, met >2 high-risk criteria. Breast implant-based reconstruction was performed in 63.0 % and 67.5 % of patients in the PMRT and non-PMRT cohorts, respectively. The 8-year median locoregional recurrence (LRR) rates were significantly lower in the PMRT cohort (5.6 %) than in the non-PMRT cohort (13.3 %) (p < 0.001). PMRT was an independent predictive factor for LRR (hazard ratio: 0.238, 95 % confidence interval: 0.127-0.446, p < 0.001).

[CONCLUSION] PMRT following BR for patients with high-risk breast cancer was associated with significantly lower LRR rates, indicating its effectiveness for improving survival in this population.