Osteosarcoma, a cancerous lesion of the bone, is quite rare. It is rapidly growing and aggressive in nature, and is generally found in children and adolescents. It is the most common bone cancer in children, and seems to occur less often in black children. About 900 cases were reported in the United States in the year 2001. Of those cases, only 10% occurred in adults over age fifty, two-thirds of which were in men.

Clinical Features
Osteosarcoma is usually discovered due to pain, disfiguration of the bone with palpable mass effect, or pathologic fracture. Pain is generally caused by impingement on the periosteum where pain-sensing nerve fibers exist. This impingement can occurr directly by the tumor or inderctly due to stretching of the periosteum. Disfiguration is caused by the rapid growth of the tumor to and past the surface of the bone, causing a lump or mass. Pathologic fracture is caused by destruction of the bone by the tumore, and its subsequent weakness at the tumor site.

Osteosarcomas generally occur spontaneously, although exposure to radiation and heritage may play a small role in its development.

Symptoms of osteosarcoma include a hard painful mass on the bone, with pathologic fracture occurring less commonly. Measurement of serum chemistry reveals an elevated serum alkaline phosphatase. On Xrays, the tumor shows as a destructive lesion with disorganized ("amorphous") calcification. The tumor commonly breaches the bony cortex into the tissues. A sunburst pattern ("radial ossification]") is also commonly seen. The tumor can either appear densely ossified ("osteoblastic") or radiolucent ("osteolytic").

Natural course of illness
Osteosarcoma tend to occur at the metaphysis of the long bones of the body - especially the distal femur, the proximal tibia, the proximal humerus, and the distal radius in that order. They grow early and rapidly, and often form localized "skip" metastases. The tumor also commonly spreads to the lungs when it begins to metastasize.

Chemotherapy and surgical removal remain the best options for treatment. If the tumor is relatively small, a limb-salvage procedure can be performed, but amputation is somethimes necessary.

Survival rates in children approach 70% if there has been no metastasis of the cancer. They drop to only 40% if the tumor has spread. (In the 1960's the survival rate was only about 15%.) Adults have somewhat lower survival rates, which are poorly defined due to the rarity of cases over age fifty.