Osteosarcoma is the uncontrolled growth of abnormal cells in bone. Although it is the most common type of bone cancer, it is rare. Osteosarcoma typically appears as a mass of abnormal bone in an arm or leg, usually near the knee or shoulder. Less often, the tumor develops in the pelvic bones, jaw, or ribs. It rarely develops in the fingers or toes. At the time of diagnosis, 10% to 20% of osteosarcomas have spread (metastasized) to another part of the body, usually the lungs. More than half of osteosarcomas develop in people between the ages of 10 and 20, usually during a growth spurt. Young people have a higher risk of developing the disease if they have had eye cancer or Li-Fraumeni syndrome. About one-third of osteosarcomas strike adults between the ages of 40 and 50. The disease is more common in men than women. Adults are at higher risk if they have a history of Paget's disease or radiation therapy for cancer.
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