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.
Watanabe
Masazumi
M
Department of Surgery, School of Medicine, Keio University, Tokyo, Japan. masazumi@med.keio.ac.jp
Yu
Shan-kang
SK
Sawafuji
Makoto
M
Kawamura
Masafumi
M
Horinouchi
Hirohisa
H
Mukai
Makio
M
Kobayashi
Koichi
K
D000071443:12E7 Antigen; D015703:Antigens, CD / Q000378:metabolism; D002277:Carcinoma / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D015815:Cell Adhesion Molecules / Q000378:metabolism; D006801:Humans; D016246:Lymphocytes, Tumor-Infiltrating; D019098:Telomerase / Q000378:metabolism*; D013945:Thymoma / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D013953:Thymus Neoplasms / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology
D000071443:12E7 Antigen; D015703:Antigens, CD; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules; D019098:Telomerase