Extraosseous osteosarcoma in a nonhuman primate (Macaca mulatta).

A case of a very rare malignant bone-forming sarcoma, which was located in the soft tissue but had no anatomic attachment to bone, is presented. This tumor originated in the subcuticular tissue over the right scapula and was histologically composed of sheets of anaplastic spindle cells that produced osteoid. The tumor recurred twice before the animal was killed. The recurrent masses produced less osteoid and were generally less differentiated histologically than the initial tumor.