Osteosarcoma is a type of bone cancer that occurs when osteoblasts mutate into cancerous cells. These cancerous cells continue to divide at an increasing rate, forming a tumor. Tumors usually develop in the growth plate, or metaphysis, the wide section of the bone that grows during childhood. Osteosarcoma can develop in any bone of the body. However, it is more likely to develop in the femur, tibia, and humerus. The most common symptoms of osteosarcoma are pain and swelling at the tumor site. Osteosarcoma usually affects patients between the ages of 10 and 20, during the adolescent growth spurt. Males and African-Americans are more likely to develop osteosarcoma.