The aim of the study was to demonstrate and analyze the expression of the following proteins, β-catenin, E-cadherin, vimentin, Ki-67, mini-chromosome maintenance 3 (MCM3), mini-chromosome maintenance 7 (MCM7), osteocalcin, cyclooxygenase-2 (COX-2), and microsomal PGE2 synthase-1 (mPGES-1) in the spontaneous osteosarcomas isolated in dogs and in humans, and to compare the results with these obtained in the established canine (D-17) and human (U-2 OS) cell lines. Immunohistochemical tests were conducted on 4 µm -thick paraffin sections and cells from established canine and human osteosarcoma cell lines. The sections and cells from cell lines were overlayed with primary antibodies. The immunocytochemical reaction was induced by 3,3 diaminobenzidinetetrahy-drochloride (DAB) solution. In a number of cases, the expression of the investigated cell markers was of comparable intensity in the cell lines and spontaneous osteosarcomas, except β-catenin and mPGES-1 in dogs. There were also no significant differences in the expression of the investigated cell markers between the group of humans and dogs. It is also worth noting that the obtained results open a perspective for developing an appropriate animal model for the study of oncogenesis in humans.

Key words: Dog, Expression of proteins, Man, Osteosarcoma cell lines