Most of fine-needle aspiration (FNA) biopsies for follicular tumors of the thyroid are deemed ‘indeterminate’ or ‘suspicious’ with regard to malignancy, even though most of these lesions are benign. Therefore, additional diagnostic markers of malignancy are needed. Telomerase activity is present in most malignant tumors. Expression of the gene encoding human telomerase reverse transcriptase (hTERT) is very closely associated with telomerase activity, this gene is overexpressed in most thyroid carcinomas. We examined telomerase activity by the telomeric repeat amplification protocol (TRAP) and hTERT gene expression by in situ hybridization (ISH) in thyroid tissue including 6 follicular carcinomas and 15 follicular adenomas. ISH for hTERT gene was performed using FNA samples from the same patients. Telomerase activity was detected in all six of the follicular carcinomas and in five (33%) of the 15 follicular adenoma tissue specimens. hTERT gene expression was detected the follicular cancer cells in all of the lesions and in one (7%) of the 15 thyroid adenomas. Moreover, we demonstrated that hTERT gene expression was occurring in four (67%) of the 6 follicular carcinoma biopsy specimens obtained using FNA. These results suggest that the detection of hTERT gene expression using ISH tissue specimens can be used to distinguish between benign and malignant follicular lesions of the thyroid, however the detection of hTERT gene in FNA samples using ISH cannot be used to definitively diagnose follicular tumors of the thyroid.

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