Pain in the affected bone is the most common symptom. This pain may initially come and go, and then gradually become more severe and constant especially at night. There may also be swelling around the affected bone. Osteosarcoma is sometimes discovered when a bone that has been weakened by cancer breaks after the person has had a minor fall or accident. Some patients may develop a limp if the tumour is in the leg or pelvis. These symptoms can be caused by many things other than cancer. However, any persistent bone pain should be checked by your child’s doctor. Symptoms are often attributed to a sporting injury.