The aim of the study is to evaluate the optimal timing of sentinel lymph node biopsy (SLNB) in patients with clinical negative axillary lymph nodes (ALNs) before neoadjuvant therapy (NAT) and the feasibility of SLNB substituting for ALN dissection in patients with positive ALNs who convert to node negative, for HER2-positive disease.

Patients receiving SLNB with dual tracer mapping in the PEONY trial were analyzed.

For 80 patients with clinical negative ALNs, the node negative rate by pathology after NAT was 83.8%. SLNB was performed after NAT in 71 patients. The identification rate of sentinel lymph nodes (SLNs) was 100%. For patients with positive ALNs before NAT, the axillary pathologic complete response rate in the dual HER2 blockade arm was significantly higher than that in the single blockade arm (p = 0.002). SLNB was performed in 71 patients. The identification rate was 100% and the false-negative rate was 17.2%. The false-negative rates were 33.3%, 14.3%, and 0 when 1, 2, and more than 2 SLNs were detected. There was no false-negative case when more than 1 SLN and the clipped nodes were removed simultaneously.

For clinical ALN negative patients, HER2-positive subtype is found to have high node negative rate by pathology and it is recommended to undergo SLNB after NAT. For patients with positive ALNs who convert to negative, the false-negative rate is high. Dual tracer mapping, more than 2 SLNs detected, more than 1 SLN identified plus the clips placed are the guarantees for lower false-negative rate.