Diagnosis of extra skeletal pleomorphic osteosarcoma in a stallion

Extra skeletal osteosarcoma affecting soft tissues below hock joint level is reported in a stallion. The animal had diffuse swelling of hind limb below the level of tibio-tarsal articulation with progressive worsening changes like exercise intolerance, pulmonary metastasis and skin ulceration. The radiographs revealed conspicuous mineralization of soft tissues, minimal periosteal reaction and metastatic nodules in lungs. Histopathology revealed presence of pleomorphic neoplastic cells with lace like osteoid deposition in between tumor cells.