Detection of matrix metalloproteinases in canine mammary tumours: analysis by immunohistochemistry and zymography.

Expression of matrix metalloproteinases (MMPs) was examined immunohistochemically (MMP-9 and -2) and by gelatin zymography (MMP-9) in 12 benign and 12 malignant canine mammary tumours. In nine of 12 benign tumours, weak expression of MMP-9 was demonstrated immunohistochemically in the cytoplasm of neoplastic cells. In the remaining three benign tumours (mixed or complex) MMP-9 expression was observed in the neoplastic luminal epithelial cells and myoepithelial cells in some areas. The neoplastic luminal epithelial cells in 12 malignant tumours reacted strongly for MMP-9. MMP-2 immunolabelling was observed in both benign and malignant tumour tissues, but was stronger in the latter. Zymography and densitometry showed that expression of MMP-9 was higher in the benign mammary tumours than in normal canine mammary tissues, but highest in the malignant mammary tumours. In benign and malignant canine mammary tumours, the zymography and densitometry results for MMP-9 accorded well with the immunohistochemical results obtained with anti-human MMP-9 monoclonal antibody.