Thyroglobulin level measurement in fine-needle aspirate for detecting metastases of neck lymph nodes in papillary thyroid cancer

Objectives The purpose of this study is to evaluate the value of fine-needle aspirate thyroglobulin (Tg) measurement in identifing neck lymph node (LN) metastases in papillary thyroid cancer (PTC), and to compare with serum Tg, cytology and biopsy results.

Methods In 225 patients who were suspected of cervical LN metastases, fine-needle aspiration was performed, and Tg concentration was measured by radioimmunoassay. Biopsy or cytology results confirmed metastases in 104 patients, and benign lesions in 100 patients. Surgical biopsy detected metastases in 12 patients having negative cytologic findings. Detection rates of aspirate Tg and serum Tg were analyzed in 156 patients.

Results Aspirate Tg level with metastatic LN was significantly higher than that of benign lesion (11595.2±33814.5 vs. 431.7±2762.3, P<0.002). Among 12 patients showing discrepancy between biopsy and cytology (all metastatic LN in biopsy), aspirate Tg level (range: 343-25000 ng/ml) was high in 8 patients (66.7%) In addition, aspirate Tg detected 3 more patients with LN metastases in whom serum Tg was undetectable (<0.1 ng/ml). Aspirate Tg revealed larger area in receiver operation characteristic (ROC) curve than serum Tg (0.954 vs. 0.622, P<0.000 and 0.008, respectively). Cut-off value of aspirate Tg in ROC curve was 7.57 ng/ml (sensitivity: 92.6%, specificity: 92.0%)

Conclusions Aspirate Tg distinguishes cervical LN metastasis quite well, and has additional value over cytology result. In addition, aspirate Tg has higher detection rate of metastatic LN than serum Tg