Immunohistochemical staining of metallothionein in canine mammary tumors: Better survival with higher expression

Metallothioneins (MT) are small proteins able to strongly bind and therefore neutralize heavy-metal, free-radical and other genotoxic compounds. A close relationship between MT and zinc-finger motif-dependent transcription factors has also been shown, with implications on cell proliferation and survival. Human malignant neoplasms (e.g. breast cancer) usually present worse prognosis with increased MT content. We therefore evaluated the immunohistochemical expression of MT in a group of 15 canine mammary gland tumors. There was no relationship between MT immunostaining and histological type or malignancy grading of the lesions. Comparison of MT immunolabelling with the overall survival of the animals revealed that MT overexpression was related to better prognosis, a contrasting finding with the human counterpart. We considered that differential MT gene expression could be responsible for this variation, as observed for some human neoplasms of distinct embryonic origin, but further investigation is required to elucidate this topic.