DefinitionOsteosarcoma is a cancerous (malignant) bone tumor that usually develops during the period of rapid growth that occurs in adolescence, as a teenager matures into an adult.Alternative NamesOsteogenic sarcomaCauses, incidence, and risk factorsOsteosarcoma is the most common cancerous (malignant) bone tumor in youth. The average age at diagnosis is 15. Boys and girls have a similar incidenceof this tumor until late adolescence, at which time boys are more commonly affected.The cause is not known. In some cases, osteosarcoma runs in families, and at least one gene has been linked to increased risk. This gene is also associated with familial retinoblastoma, a cancer of the eye that occurs in children.Osteosarcoma tends to occur in the bones of the:Shin (near the knee)Thigh (near the k