Telomerase activity is present in most malignant tumors and provides a mechanism for unlimited replication of neoplastic cells. This study was undertaken to investigate the expression of the gene encoding human telomerase reverse transcriptase (hTERT), the telomerase catalytic subunit gene in lung carcinoma, by in situ hybridization (ISH). hTERT is associated with telomerase activity, and overexpressed in most lung carcinomas. We assayed hTERT gene expression by ISH to study telomerase activity in lung carcinomas of 27 patients, and compared these results with those of telomerase activity by telomeric repeat amplification protocol (TRAP) assay. TERT gene expression by ISH was detected mainly in the nuclei of lung carcinoma cells. Some specimens showed a significant expression in only infiltrating lymphocytes. hTERT gene expression by ISH was found in 16 of 27 (59%) cases. On the other hand, telomerase activity by TRAP assay was detected in 21 of 27 (78%) cases. In 7 cases, TRAP assay detected telomerase activity, but ISH did not detect hTERT expression. TRAP assay might detect telomerase activity in not only carcinoma cells, but also in infiltrating lymphocytes. Our findings therefore suggest that ISH-based analysis of hTERT gene expression is superior to TRAP assay as a means of determining telomerase status during carcinogenesis.

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