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

Abstract 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 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.