The Role of <scp>FNA</scp> ‐ <scp>CYFRA</scp> 21‐1 in Cervical Lymph Node Metastasis of Differentiated Thyroid Cancer

ABSTRACT Objective To investigate the role of fine needle aspiration thyroglobulin (FNA‐TG) and fine needle aspiration cytokeratin 19 fragment antigen 21‐1 (FNA‐CYFRA 21‐1) in the diagnosis of cervical lymph node metastasis of differentiated thyroid carcinoma (DTC), then analyze whether different neck lymph node compartmentalization affected the cut‐off values of FNA‐TG and FNA‐CYFRA 21‐1. Methods One hundred and sixteen lymph nodes with suspicious ultrasound signs between September 2023 and September 2024 were analyzed, and the lymph nodes were classified into central lymph nodes and lateral neck nodes, and all lymph nodes underwent fine needle aspiration cytology (FNAC), FNA‐TG, and FNA‐CYFRA 21‐1 preoperatively. Differences in the levels of FNA‐TG and FNA‐CYFRA 21‐1 in the lateral neck nodes and central lymph nodes were analyzed, and the optimal cut‐off values of the two were calculated to further analyze the value of FNAC, FNA‐TG, and FNA‐CYFRA 21‐1 for diagnosis alone and in combination. Results In the non‐metastatic lymph node group, the difference in FNA‐TG levels between the lateral neck zone and the central zone was statistically significant. The levels of FNA‐CYFRA 21‐1 were not affected by the zoning of the cervical lymph nodes. In the lateral neck region, the area under the diagnostic curve was highest for the combination of the three. Conclusions FNA‐CYFRA 21‐1 is valuable in DTC cervical lymph node metastasis and can assist in the diagnosis of FNAC and FNA‐TG, especially in suspected centralized lymph nodes that are not diagnosed preoperatively. Level of Evidence 3.