Combined-type osteosarcoma in a rhesus macaque.

A femoral mass from a 15-year-old rhesus macaque was evaluated. Grossly, the mass consisted of a large, osteolytic focus in the distal femur, a gelatinous core of neoplastic tissue in the medullary cavity, and an invasive mass-obliterating musculature of the thigh. On histopathologic evaluation, three neoplastic mesenchymal cell populations, osteoblasts, fibroblasts, and primitive mesenchymal cells were identified. The mass was diagnosed as a combined type osteosarcoma. To our knowledge, this is the first osteosarcoma in a rhesus macaque with this subclassification.