Osteosarcoma. False-colour computed tomography (CT) scan of the knee joints showing osteosarcoma (malignant bone tumour) located in the tibia at left of image. In this front view, the head of the tibia bone of the leg (centre left), just below the knee joint, is cancerous (green). Swelling is seen in soft tissues around the diseased bone. Osteosarcoma occurs most frequently in children; in the elderly it is a late complicaton of Paget's disease. It commonly affects long bones of the leg or arm, around the knee, hip, or shoulder. The cancer may spread to the lungs and liver. Treatment with anticancer drugs usually also involves the amputation of the affected limb.