Introduction: Sentinel node biopsy (SNB) has been increasingly performed for patients with lymph node (LN)-positive (cN1) breast cancer that converted to LN-negative (ycN0) status after neoadjuvant chemotherapy (NAC). This study aimed to clarify the SNB avoidance rates using fine needle aspiration cytology (FNAC) for metastatic LNs after NAC. Methods: This study included 68 patients with cN1 breast cancer undergoing NAC from April 2019 to August 2021. Patients with biopsy-proven metastatic clip-marked LNs (clipped LNs) underwent eight cycles of NAC. Ultrasonography (US) was performed to evaluate the effect of the treatment on the clipped LNs, and FNAC was performed after NAC. Patients with ycN0 status determined using FNAC underwent SNB. Those with positive results for FNAC or SNB underwent axillary LN dissection. Histopathology results and FNA were compared for clipped LNs after NAC. Results: Of the 68 cases, 53 were ycN0 and 15 were clinically positive LNs after NAC (ycN1) on US. Further, 13% (7/53) of all ycN0 and 60% (9/15) of all ycN1 cases showed residual metastasis in the LNs on FNAC. Conclusion: FNAC was diagnostically useful for patients with ycN0 status on US imaging. Using FNAC for LNs after NAC helped avoid unnecessary SNB in 13% of the cases.

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