title: Thymic epithelial tumor with heart metastasis in a horse.
abstract: Thymic malignancy is rare in horses. Thymic epithelial tumor was diagnosed in an 18-year-old mare with invasion and metastasis to the pericardium and heart. At necropsy, the cranial thoracic cavity was obliterated by a large mass located in the thymic region and the right atrium was also expanded and effaced by a similar mass. Histologically, the neoplasm was composed of sheets of spindle cells with intraparenchymal Hassall's corpuscles and formation of pseudorosettes around blood vessels compatible with type A thymic epithelial tumor according to World Health Organization classification. The neoplastic cells were diffusely immunoreactive for cytokeratin and negative for vimentin, S100, neuron specific enolase, glial fibrillar acidic protein, chromogranin A, synaptophysin, CD3 and CD79a markers. To the authors' knowledge, cardiac invasion and distinct histological pattern of pseudorosette formation have not been described in equine thymic epithelial tumors previously.
authors.affiliation: California Animal Health and Food Safety Laboratory, San Bernardino Branch, University of California, Davis, 105 West Central Avenue, San Bernardino, CA 93408, USA.
authors.forename: Farshid
authors.initials: F
authors.lastname: Shahriar
authors.forename: Janet
authors.initials: J
authors.lastname: Moore
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