The average age of diagnosis is 15 years old. Boys and girls have a similar incidence of this tumor until late adolescence at which time boys predominate. The specific cause of osteosarcoma is not known.
Evidence suggests that osteosarcoma can run in families.
The gene involved in familial retinoblastoma appears to be a defective tumor inhibitor gene and is associated with other tumors including osteosarcoma. The end of the bone in which they occur is the area of greatest change and highest 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.