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Thymic carcinomas, type C thymomas, category II thymic tumours

Definition

Thymic tumours with definite atypia. Features are not specifically organotypic to the thymus. The diagnosis therefore requires the main mass to be located in the anterior mediastinum and a lack of a possible primary tumour elsewhere3. Immature T-lymphocytes are absent. Any T lymphocytes are mature and are usually admixed with plasma cells.

Epidemiology

Thymic carcinomas account for 18% of primary thymic epithelial neoplasms5 and 6% of primary anterior mediastinal neoplasms6.

Differential diagnosis

Positivity for EMA occurs outside Hassall corpuscles in thymic carcinomas but not in thymomas, and is therefore an indication of frank malignancy.

p53 and bcl-2 immunoreactivity are significantly higher in thymic carcinomas than in thymomas. CD5 is commonly positive in thymic carcinomas but not in thymomas.

Prognosis

Survival is poor: 57%, 40%, 28-48%, 27% and at 1, 3, 5 and 10 years respectively7. An infiltrating margin and a mitotic count greater than 10/10HPF and lack of a lobular growth pattern correlate highly with poor survival7. Well-differentiated squamous, mucoepidermoid and basaloid carcinomas seem to have a better prognosis than lymphoepithelioma-like, small cell / neuroendocrine, sarcomatoid and clear cell carcinomas7.

References

J Rosai et al. Histological typing of tumours of the thymus. WHO International histological classification of tumours. Springer-Verlag, second edition, 1999.

2Hattori, H., H. Tateyama, et al. (2000). "PE-35-related antigen expression and CD1a-positive lymphocytes in thymoma subtypes based on Muller-Hermelink classification.An immunohistochemical study using catalyzed signal amplification." Virchows Arch 436(1): 20-7.

3Pan, C. C., W. Y. Chen, et al. (2001). "Spindle cell and mixed spindle/lymphocytic thymomas: an integrated clinicopathologic and immunohistochemical study of 81 cases." Am J Surg Pathol 25(1): 111-20.

4Hishima, T., M. Fukayama, et al. (2000). "CD70 expression in thymic carcinoma." Am J Surg Pathol 24(5): 742-6.

5Chen, G., A. Marx, et al. (2002). "New WHO histologic classification predicts prognosis of thymic epithelial tumors: a clinicopathologic study of 200 thymoma cases from China." Cancer 95(2): 420-9.

6Liu, H. C., W. H. Hsu, et al. (2002). "Primary thymic carcinoma." Ann Thorac Surg 73(4): 1076-81.

7Suster, S. and J. Rosai (1991). "Thymic carcinoma. A clinicopathologic study of 60 cases." Cancer 67(4): 1025-32.

This page last revised 24.12.2004.

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