Case report: osteolytic osteosarcoma in a German Shepherd bitch.

Necropsy of a six year old female German Shepherd revealed the presence of a large oval mass in the thoracic cavity originating from the thickened proximal portion of the right fourth rib. Osteolytic osteosarcoma was diagnosed on the basis of gross appearance, presence of many pleomorphic spindle cells, containing pink stained intracytoplasmic granules in cytological preparations of impression smears of the tumor and histopathology. The tumor was considered highly malignant and was characterized by an abundant osteoblastic and connective tissue stroma with extreme cellular pleomorphism including giant cells, atypical mitoses and occasional trabeculae of tumor bone and osteoid. Metastases were found in the lung and spleen. Electron microscopy was carried out to support the diagnosis.