Discordant Breast and Axillary Pathologic Response to Neoadjuvant Chemotherapy

Introduction Neoadjuvant chemotherapy (NAC) for breast cancer has the advantage of determining in vivo response to treatment, enabling more conservative surgery, and facilitating the understanding of tumor biology. Pathologic complete response (pCR) after NAC is a predictor of improved overall survival. However, some patients demonstrate a discordant response to NAC between the breast and axillary nodes. This study was designed to identify factors that correlate to achieving a breast pCR without an axillary node pCR following NAC and explore the potential clinical implications.Methods The National Cancer Database was used to identify patients diagnosed with clinical T1-4, N1-3 breast cancer between 2004 and 2017. Patients underwent NAC followed surgical resection of the breast cancer and axillary node surgery. Multivariable analyses were used to identify clinical and pathologic factors associated with discordant pathologic response.Results In total, 13,934 patients met the inclusion criteria. Of these, 4292 (30.8%) patients demonstrated a breast pCR without a corresponding axillary pCR on final pathology. After adjusting for covariates, factors associated with higher discordance between axillary response in our cohort of breast pCR patients included older age (=54), treatment at a community facility, T1 tumors, HR-positive, HER2 negative, low-grade tumors, and cN2/3 disease.Conclusions Discordance between breast and axillary pCR is not infrequent and may be related to a number of patient-related factors and tumor characteristics impacting nodal response to NAC. Further investigation into differing responses to NAC is warranted to better understand the mechanism of this phenomenon and to determine how these findings may influence treatment.