Osteosarcoma of bone.

The definition of osteosarcoma requires that a malignant tumor of bone produce osteoid or bony matrix. With this as a basic definition, osteosarcoma of bone can be divided into several clinicopathologic entities based on clinical, roentgenographic, and pathologic features. The tumors can be broadly divided into those arising within the bone and those arising on the surface of bone. Most intraosseous osteosarcomas are high-grade malignant tumors that occur in children and adolescents. A small number occur in older patients, and they may be related to a preexisting condition, such as Paget's disease or radiation. The site of the lesion has prognostic importance. Osteosarcoma of the jaws is associated with an especially good prognosis, whereas the same kind of tumor involving the skull has a very poor prognosis. Most osteosarcomas of the surface of bone are well or moderately differentiated and are associated with an excellent prognosis.