Sentinel Lymph Node Biopsy After Neoadjuvant Chemotherapy in Patients Presenting With Locally Advanced Breast Cancer

PURPOSE To prospectively determine the false-negative rate (FNR) of sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy (NAC) in patients with locally advanced breast cancer (LABC). METHODS Patients with cT4 and/or cN2/N3 breast cancer with a nodal complete response (cN0) after NAC were eligible. SLNB was performed with dual-tracer mapping; nodal clipping was not required. All patients had a completion axillary lymph node dissection. FNR calculations were based on the patients with adequate mapping (ie, ≥3 SLNs or <3 SLNs plus clipped node). Of the planned 150 patients, we anticipated that 84 patients would have adequate mapping and that 47 would have residual disease after NAC (nodal pathologic complete response [pCR] rate: 45%). Assuming a true FNR of 10%, we estimated that this sample size would allow estimation of FNR within a margin of error (95% CI half-width) of ±8.6%. RESULTS From August 2017 to December 2025, 456 patients were screened for eligibility; 369 (81%) became cN0 after NAC and 145 were enrolled in the study. Of these, 44% of patients had inflammatory breast cancer (cT4d), 23% had other cT4 disease, 12% had cN2 disease, and 21% had cN3 disease. At least 1 SLN was identified in 108 patients (74%), of whom 87 had either ≥3 SLNs (n = 82) or 1-2 SLNs with a clipped node retrieved (n = 5). Of 87 patients with adequate mapping, the nodal pCR rate was 46%; of 47 (54%) with residual nodal disease, one false-negative SLN was observed, yielding an SLN FNR of 2.1% (95% CI, 0.1 to 12.7). CONCLUSION In a prospective cohort of patients with LABC, the SLN identification rate was 74% and the FNR was 2.1%, suggesting that SLNB may be an appropriate method to stage the axilla in LABC after downstaging with NAC.