Morphological and immunohistochemical studies of spontaneous mammary tumours in Siberian hamsters (Phodopus sungorus).

Mammary tumours from 12 domestic Siberian hamsters (11 females, 1 male) were examined. Histopathology revealed three subtypes: simple adenoma, tubulopapillary carcinoma, and complex carcinoma. In five cases of malignant mammary tumour, focal infiltration into the surrounding fibrous connective tissue was present; however, no invasion of either lymphatics or blood vessels was observed. Apocrine secretion from neoplastic luminal epithelial cells was prominent in all tumours. Expression of oestrogen receptor alpha, progesterone receptor, and androgen receptor was evaluated immunohistochemically in neoplastic epithelial cells. Ten of the 12 tumours were positive for androgen receptor and all were negative for progesterone receptor. Five tumours expressed oestrogen receptor alpha.