Occurrence of trichoepithelioma in a cat: Histopathologic and immunohistochemical study.

Trichoepitheliomas are benign follicular appendage tumors with differentiation to all three segments of the hair follicle. A 2 years old female domestic short hair cat presented with a mass on the tail. The mass was surgically excised and for histopathologic and immunohistochemical studies, was sent to Department of Pathology. Histologically, the tumor was encapsulated and consisted of many islands of follicular epithelium and also cysts structures which varied in size and shape. The cells of epithelium islands were round to oval and had variable amounts of slightly, eosinophilic cytoplasm and euchromatic nuclei. The cystic structures were lined by a complex layer of squamous epithelium. Often, cells under went an abrupt transition between basal layers and keratinization without the development of a granular cell layer. No tendency of malignancy was seen in this case. According to mentioned characteristics, trichoepithelioma was diagnosed. By immunohistochemical study it was confirmed that this tumor had epithelial origin because squamous tumor cells reacted with the pan-cytokeratin antibody. The expression of β-catenin was predominately cytoplasmic and also together with numerous positive nuclei but membranous expression was inconsistenet. Distribution of neoplastic cells with β-catenin expression was more than 75% and labeling intensity was strong in both cytoplasm and nuclei. According to author's knowledge, this is the first report of trichoepithelioma in cat in Iran and also investigation of β-catenin expression in feline trichoepithelioma in veterinary literature.