Telomerase activity (TA) has been shown highly expressed in various solid malignant neoplasms, but only rarely in benign tumor or normal tissues. Most reports examined TA by the qualitative method, telomeric repeat amplification protocol (TRAP) assay. We examined TA in tissues of thyroid neoplasm by quantitative method to establish whether TA was a useful marker for preoperative differential diagnosis of thyroid tumors. TA was measured by the quantitative method, TRAP assay, fluorescence based TRAP method in 32 frozen tissues of thyroid tumors (17 malignant, 15 benign). Cut-off values in TA were 0 unit and 9 units from mean ± 2SD of TA in benign thyroid tumors. Mean (SD) TA levels in benign thyroid tumors and thyroid carcinomas were 2.06 (3.58) units and 30.5 (38.2), respectively. Mean TA of carcinomas was significantly higher than that of benign disease in thyroid tumors (p=0.0092). The sensitivity of the malignancy was 64.7% (cut-off <0) (p=0.162), 52.9% (cut-off <9) (p=0.0048). TA in thyroid carcinoma was significantly correlated with UICC stage (p=0.029), and slightly correlated with tumor size, pN and M. Positive rate of TA in microfollicular adenoma was slightly higher than that in macrofollicular adenoma. Conclusively, quantitative TA might be a useful marker for differential diagnosis between benign and malignant thyroid tumors.

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