Metallothionein expression in canine and feline mammary and melanotic tumours

Moderate to strong immunohistochemical metallothionein (NIT) positivity (NI T expression) is associated with a poor prognosis in some human tumours. Th e aim of this study was to determine MT expression in mammary tumours and c utaneous melanomas in dogs and cats. Canine (67) and feline (47) mammary tu mours, and cutaneous melanomas (canine 40, feline 26) were immunolabelled w ith MT monoclonal antibody E9. The overall incidence of MT expression of th ese tumours was similar to that observed in various human neoplasms. Howeve r, a striking interspecies difference was detected. In dogs,NIT expression occurred in 100% of benign and 57% of malignant mammary tumours. In cats, h owever, 30% of malignant mammary tumours expressed NIT but benign mammary t umours and cases of fibroadenomatous hyperplasia did not. Moderate to stron g MT immunoreactivity was detected in 30% of benign and 25% of malignant cu taneous melanomas in dogs, and in 6% of malignant melanomas in cats. The fi ndings in feline mammary tumours resembled findings reported in human breas t cancer, but the cause of tumour-associated MT expression is unknown. Stud ies are in progress to determine whether the NIT state (apo [metal-free] or holo [metal-bound]) accounts for the paradoxical association of MT express ion with individual types of tumours and the animal species in which they a rise. (C) 2001 Harcourt Publishers Ltd.