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Background: Telomerase is a nucleoprotein complex that caps the physical termini of all eukaryotic chromosomes. It is suggested that telomerase play important roles in unlimited cell division acquisition of the malignant phenotype. We studied the relation of telomerase activity in thymoma and thymic carcinoma to the clinicopathological features of these lesions., Methods: Tissue specimens were surgically resected from patients with thymoma and thymic carcinoma. Telomerase activity was evaluated according to a modified telomeric repeat amplification protocol (TRAP) assay., Results: Telomerase activity was detected in all thymic epithelial tumors. The activity (mean +/- SD: unit/microgram.protein) in thymoma (n = 17) was significantly higher than that in thymic carcinoma (n = 7) [431.8 +/- 400.1 vs. 68.8 +/- 39.8: p < 0.01]. Telomerase activities in thymoma and thymic carcinoma were significantly higher than that in primary lung adenocarcinoma (33.5 +/- 39.2: n = 47), studied as control (p < 0.01). In patients with thymoma, telomerase activity did not correlate with tumor stage according to Masaoka classification (p = 0.776). In patients with thymic carcinoma, however, telomerase activity positively correlated with tumor stage (p = 0.02). In thymoma, telomerase activity positively correlated with the ratio of induced lymphocytes according to Rosai's classification (p = 0.045)., Conclusion: In thymoma, telomerase activity reflects the presence of immature T-cell lymphocytes in tumor tissue rather than tumor stage or malignant phenotype. In thymic carcinoma, telomerase activity derived directly from cancer cells may relate to tumor stage.

The mechanisms of ectopic enzyme and enzyme inhibitor-production in neoplastic tissues were investigated. No evidence was obtained to suggest any difference in the structural genes of amylase-producing tumors and normal lymphocytes. mRNA sequence coding for amylase precursor in tumor tissues was identical to that of salivary amylase, suggesting that the amylase in amylase-producing tumors was identical to, or closely resembled the amylase in salivary gland. High incidence of elevation of serum pancreatic secretory trypsin inhibitor (PSTI) was observed in patients with various malignant tumors. PSTI-positive malignant cells were also frequently found in malignant tissues. A comparison of human PSTI mRNA sequence with mouse epidermal growth factor (EGF) mRNA sequence showed that they were 46% homologous. Human PSTI stimulated [3H]thymidine incorporation into DNA in human fibroblasts at concentrations present in human serum.