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thymic epithelial tumors

Tuesday 13 September 2011

Differential diagnosis

Rarely, primary thymic epithelial tumours may mimic mesothelioma by diffusely infiltrating the pleura to form thickened, plaque-like areas.

In the series of Attanoos et al., the thymic tumours differed in their World Health Organization type, but were classified as thymomas rather than thymic carcinomas.

The thymic epithelial component variably expresses CK5/6, calretinin, thrombomodulin and CD20, but the main distinction from mesothelioma is made on the pattern of the tumour and the lymphoid component of immature T cells, expressing CD3, CD5, terminal deoxynucleotidyl transferase (TDT, TdT) and CD99, with a high proliferation fraction.

Immunochemistry

- proteasome β subunit β5t

  • Recently, a proteasome β subunit expressed exclusively in thymic cortical epithelial cells was discovered in mice and humans.
  • This subunit, designated β5t, is a component of the thymoproteasome, a specialized type of proteasome implicated in thymic positive selection.
  • β5t is expressed in most type B and in some type AB thymomas and is a marker useful in differentiating type B3 thymomas from thymic carcinomas when used in combination with other diagnostic markers.

See also

- thymic tumors

References

- Expression of Proteasome Subunit β5t in Thymic Epithelial Tumors. Yamada Y, Tomaru U, Ishizu A, Kiuchi T, Marukawa K, Matsuno Y, Kasahara M. Am J Surg Pathol. 2011 Sep;35(9):1296-304. PMID: #21836487#