Regional Nodal Irradiation for Clinically Node-Positive Breast Cancer Patients With Pathologic Negative Nodes After Neoadjuvant Chemotherapy.

INTRODUCTION: Neoadjuvant chemotherapy (NAC) is increasingly used for operable breast cancer (BC). Appropriate radiation therapy (RT) fields (ie, whole breast [WB] ± regional nodal irradiation [RNI]) in patients who were clinically node positive (cN1) but convert to pathologically node negative (ypN0) after NAC are unknown and the subject of the accruing NSABP B-51 trial. We sought to compare outcomes between WB RT with or without RNI following breast conservation and sentinel lymph node biopsy (SLNB) alone in cN1, ypN0 women following NAC. PATIENTS AND METHODS: We identified all BC patients with cN1, ypN0 who underwent NAC followed by lumpectomy and SLNB between 2006 and 2015 in the National Cancer Database. RNI utilization was evaluated using Cochran-Armitage test. Overall survival between WB RT alone versus WB + RNI was compared using Kaplan-Meier with and without propensity score-based weighted adjustment and multivariable (MVA) Cox proportional hazards. RESULTS: From 2006 to 2015, RNI use increased from 48.13% to 62.13% (Pfor trend <.001). The 10-year survival for WB alone versus WB + RNI was 83.6% and 79.5%, respectively (P= .14). On MVA analysis, the addition of RNI compared to WB alone was not associated with a survival benefit (WB vs. WB + RNI: hazard ratio 0.80, 95% confidence interval, 0.58-1.11, P= .19). Results were unchanged after propensity score-based adjustment. CONCLUSION: For women with cN1 BC who convert to ypN0 following NAC and breast conserving surgery with SLNB alone, more extensive RNI may not provide a long-term survival benefit. Prospective validation via the NSABP B-51 trial will be essential.