Osteosarcoma 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.

Osteosarcoma is the most common cancerous (malignant) bone tumor in youth. The average age at diagnosis is 15. Boys and girls have a similar incidence of 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 knee)
• Upper arm (near the shoulder)

This cancer occurs most commonly in larger bones and in the area of bone with the fastest growth rate. Osteosarcoma can occur in any bone, however.

Although it is rare, osteosarcoma can occur in adults.