Immunohistochemical study of hormonal receptors and cell proliferation in normal canine mammary glands and spontaneous mammary tumours

The expression of hormone receptors and their relationship-to cell prolifer ation in six samples of normal canine mammary tissue, and 11 benign and 10 malignant mammary neoplasms from female dogs were assessed by immunohistoch emistry in formalin-fixed paraffin-embedded samples, by using monoclonal an tibodies against progesterone and oestrogen receptors, and nuclear antigen Ki-67 (MIB-1). Malignant tumours negative for progesterone receptors prolif erated at higher rates than progesterone receptor-positive tumours, suggest ing that the progression towards malignancy in spontaneous mammary tumours is accompanied by a decrease in hormonal steroid dependency. Only one malig nant tumour was positive for oestrogen receptors.