Giant cell-rich osteosarcoma of tibia in a dog: a pathological and immunohistochemical study

Osteosarcoma is determined as a bone matrix-producing malignant mesenchymal tumor. However, it is relatively rare among different species of domestic animals, but it corresponds about 85 % of all malignant bone tumors in dogs. Nevertheless, the giant cell-rich osteosarcoma (GCRO) is a rare subtype of the osteosarcoma, which to our knowledge has not yet been reported in dogs. This report describes a GCRO in the tibia of a six and half-year-old, spayed, 41 kg, female, Scottish deerhound dog with a history of a mass on the tibia and severe lameness being observed by the owner. Histologically, the tumor was characterized by numerous multinucleated giant cell nests separated by small bundles of pleomorphic to polygonal cells. Between the spindle cells, osteoid was rare and organized in thin strands. Immunohistochemical stains for vimentin were positive, with no detectable cellular staining for cytokeratin. A GCRO was concluded in this case. The dog died 1 week after the biopsy.