Osteosarcoma is a malignant bone tumor that usually develops during the period of rapid growth which occurs in adolescence, as a teenager matures into an adult.

Osteosarcoma is the most common 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 which occurs in children. It appears to be a defective tumor inhibitor gene.

Osteosarcoma tends to occur in the bones of the thigh (distal end, near the knee), upper arm (proximal end, near the shoulder), and shin (proximal end, near the knee). This cancer occurs most commonly in larger bones and in the area of bone with fastest growth rate. Osteosarcoma can occur in any bone, however.

The most common symptom initially is pain. As the tumor grows, there may be visible swelling and limitation of motion. Tumors in the legs cause limping, while those in the arms cause pain on lifting. Swelling over the tumor may be warm and slightly reddened.

• Bone pain
• Tenderness, swelling, or redness at the site of the bone pain
• The first sign may be a bone fracture. The tumor may cause weakness in the affected area of the bone. A fracture at the site of the tumor is called a "pathological fracture," which occurs after what often seems like a routine movement. For example, a young athlete who breaks an arm during a routine throw should be tested to ensure there is no underlying bone problem, such as a tumor or cyst.

• X-ray of the affected area
• CT scan of the affected area
• Blood tests
• CT of the chest to see if the cancer has spread to the lungs
• Open biopsy (at time of surgery for diagnosis)
• Bone scan to see if the cancer has spread to other bones