Osteosarcoma in Paget disease of bone. Light micrograph showing thick trabeculae of Pagetic bone at left and high-grade osteosarcoma producing delicate osteoid at right. Paget disease of bone is a risk factor for the subsequent development of osteosarcoma. Most osteosarcomas arising in individuals over the age of 40 years occur in the setting of polyostotic Paget disease. The usual locations are the pelvis, humerus (upper arm bone), femur (thigh bone), tibia (shin bone), and skull. The prognosis is extremely poor.