A poorly-differentiated squamous cell thymoma in a chicken with lymphoma.

Thymic carcinomas are rare in birds. A poorly-differentiated squamous cell thymoma was found in a chicken in association with a lymphoma caused by Marek's disease. Immunohistochemical techniques with different tumour markers were applied in order to determine the histogenesis of the thymic tumour cells. A positive immunoreaction of the tumour cells to cytokeratin, considered a specific marker for epithelial tumours, confirmed the diagnosis of a thymoma.