Impact of Post-Mastectomy Radiation Therapy for Sentinel Lymph Node Micrometastases in Early-Stage Breast Cancer Patients

BACKGROUND: The association of radiotherapy with breast cancer survival in patients who underwent a mastectomy and had micrometastases in the sentinel lymph node is unclear. MATERIAL/METHODS: The survival benefit of radiotherapy was examined in patients with T0/1-T2N1mi breast cancer undergoing mastectomy plus sentinel lymph node biopsy (SLNB). Kaplan-Meier curves were employed for survival analysis and competing risk analysis, and a propensity score matching (PSM) cohort was enrolled to investigate whether such patients benefit from radiotherapy. RESULTS: We identified 2864 patients in the SEER database from 2004 to 2015. All eligible patients were divided into the radiotherapy and the no-radiotherapy cohorts. With the median follow-up of 53 months, 5-year breast cancer-specific survival (BCSS) was 94.4% vs 95.2% (P=0.135), and 5-year overall survival (OS) was 91.2% vs 90.1% (P=0.466) in the radiotherapy cohorts and no-radiotherapy cohorts, respectively. The results of the competing risk analysis showed a comparable 5-year cumulative incidence of breast cancer-specific death (BCSD) in the radiotherapy and no-radiotherapy groups (5.5% vs 4.7%, P=0.107) but a higher 5-year cumulative incidence of other causes of death (OCD) in the no-radiotherapy cohort (3.3% vs 5.3%, P=0.011). No significant difference was observed for BCSS or OS in the PSM cohort. CONCLUSIONS: Radiotherapy has no benefit for patients with T0/1-T2 breast cancer undergoing mastectomy with N1mi disease on SLNB. This analysis provides evidence that radiotherapy may safely be omitted in this group of patients.