Background: Neoadjuvant chemotherapy (NAC) may downstage axillary disease in node-positive breast cancer. Several clinical trials have shown that sentinel lymph node (SLN) surgery after NAC is feasible for these patients. We sought to evaluate the use of SLN surgery and ALND in cN1 patients undergoing NAC. Methods: We identified all patients with biopsy-proven cN1 breast cancer treated with NAC at our institution between January 2009 and December 2017. Approximated biologic subtype was determined by estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) status. Cochran–Armitage trend and Chi square tests were used for statistical analysis. Results: Of 430 cN1 patients treated with NAC, 93 (22%) underwent SLN surgery only, 100 (23%) underwent SLN and ALND, and 237 (55%) underwent ALND only. The use of SLN surgery (± ALND) increased from 28% in 2009 to 86% in 2017 (p < 0.001), while the performance of ALND decreased from 100% in 2009 to 38% in 2017 (p < 0.001). Among SLN+ patients who underwent ALND, disease was limited to the SLNs in 25/73 (34%) patients. The nodal pathologic complete response rate was 46% and varied by tumor subtype (p < 0.001). Among patients undergoing SLN surgery, ALND was avoided in 48% of patients overall and varied by biologic subtype: 55% ER−/HER2+, 61% ER+/HER2+, 62% ER−/HER2−, and 31% ER+/HER2− (p = 0.001). With short-term follow-up, no nodal recurrences have occurred in patients without ALND. Conclusions: We observed a significant shift in axillary surgery for cN1 breast cancer patients treated with NAC, with increasing use of SLN surgery to assess nodal treatment response, and decreasing use of ALND.
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