Metastatic giant cell osteosarcoma in a cat.

A four-year-old male Persian cat was referred with three weeks history of progressive lameness due to a rigid osseous mass with 3.50×2.50×2.00 cm in dimensions in his left arm. In the histopathological evaluation of bone biopsy, two distinct populations of cells including multinucleated giant cells and oval cells which embedded in a fibro-osseous stroma and surrounded by lamellar bone trabeculae were observed. At necropsy, multiple metastatic nodules with different sizes unveiled in the liver and spleen. Microscopically, those tumor cells which already described in the bone lesion were also infiltrated to the liver and spleen. The neoplastic cells had no immunoreaction to CD68, desmin, alpha smooth muscle actin, S100, CD20, CD3 and pancytokeratin, but only a few cells had reaction to vimentin were similar to fibroblasts.