Malignant trichoepithelioma in the prepuce of a Pitbull breed dog

A 12-year-old, male Pitbull dog was referred for a voluminous mass in the prepuce. Phys- ical examination revealed an oval mass, cauliflower-shaped with an alopecic and ulcer- ated surface. Cytological examination revealed large amounts of neutrophil granulocytes and keratinised cells with several atypic features, such as anisokaryosis, anisocytosis, anisonucleosis, nuclear and cytoplasmic vacuolation, and mitoses. Histopathology of the surgically excised sample showed malignant epithelial cells arranged in trabeculae, islands and cords showing differentiation of all three segments of a hair follicle. In addi- tion, there were foci of trichogenic differentiation with intracytoplasmic trichohyalin granules, and the presence of ghost cells in the epithelial islands. The macroscopic and histological features led to the diagnosis of a malignant trichoepithelioma according to the characteristics reported in the literature, except for the unusual localisation in the canine prepuce.