Immunohistochemical study of a non-invasive canine thymoma: a case report.

We describe a case of canine thymoma in an 11-year-old pure-bred female Spanish Mastiff. On post-mortem examination a big mass was found in the thoracic cavity. Histologically the neoplastic parenchyma showed great structural variability; the principal findings included the presence of tumour cells forming cords or sheets, cystic formations, Hassall-corpuscle like squamous formations, and small or intermediate calibre vessels encircled by areas with eosinophilic material and lymphocytes. In order to determine the histogenesis of the thymic neoplasia we used immunohistochemical techniques specific for different markers: cytokeratins, vimentin, desmin and neuron specific enolase. A strong positive immunoreaction of tumour cells to wide spectrum cytokeratins confirmed the epithelial origin of the neoplasia.