PTH and osteosarcoma: Although no evidence of osteosarcoma has been observed in humans treated with PTH (18, 58), PTH should be avoided in patients with elevated risk of osteosarcoma and a history of cancer, including adolescents in whom the epiphyses have not yet closed, those with Paget’s disease or prior skeletal radiation, and patients with unexplained increases in alkaline phosphatase (59).