Testicular leiomyosarcoma and marked alopecia in a cryptorchid ferret (Mustela putorius furo).

A 3.5-year-old male ferret, bought as male castrated, was presented to the veterinarian with marked alopecia of back, neck, abdomen and tail, a pronounced sexual behaviour and weight loss. An inguinal mass of about 2.5 cm in diameter was diagnosed as potentially tumorous inguinal testicle by ultrasound and fine-needle aspiration. Adrenal glands and prostate were ultrasonographically unremarkable. The surgically removed cryptorchid testicle contained a greyish tumour that was histologically composed of spindle-shaped cells with elongated nuclei, embedded in a fibro-vascular stroma. Up to two mitotic figures per high power field were noted. Additionally, an interstitial cell hyperplasia and marked reactive proliferation of a collagen-rich fibrous tissue were observed. Tumour cells were positive for α-smooth muscle actin, desmin, and occasionally vimentin and S-100, leading to the diagnosis of an intratesticular leiomyosarcoma. As an adrenal-associated endocrinopathy was excluded and a complete fur recovery was observed after removal of the cryptorchid testicle the alopecia was eventually due to hormones produced by the hyperplastic interstitial (Leydig) cells.