Enhanced expression of telomerase activity in thymoma and thymic carcinoma tissues: a clinicopathologic study

Background: Telomerase is a nucleoprotein complex that caps the physical termini of all eukaryotic chromosomes. Because most malignant cells and reproductive cells have telomerase activity, which elongates telomeric DNA, telomerase may play important roles in unlimited cell division acquisition of the malignant phenotype. The current study examined the relation of telomerase activity in thymoma and thymic carcinoma with the clinicopathologic 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 assay. Paraffin sections of tumor were immunostained by MIC2 antibody, a marker of immature T cells.

Results: Telomerase activity was detected in all thymic epithelial tumors. The activity (mean +/- SD; unit per microg 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 a 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). MIC2-positive lymphocytes were identified in all cases of thymoma (n = 12). In contrast, lymphocytes infiltrating thymic carcinoma did not react with MIC2.

Conclusions: 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.