Abstract
Osteosarcoma is one of the most important bone tumors of human beings and pet animals. It is a rapidly progressive, early metastasize, osteolytic, highly fatal tumor. It may arise from central medullary osteoblasts, peripheral periosteal or perichonderal cells, and extra skeletal tissues or may have a pluripotent potential. A Shirazi Native breed cat was examined for the presence of multilocular lobulated partially encapsulated masses in the external ear. The excised tissue revealed anaplastic, chondroblast and osteoblast mesenchymal differentiations associated with hypercellularity, pleomorphism and increase in mitosis, consistent with chondroblastic osteosarcoma.