[Osteosarcoma in rats receiving long-term PTH injection]

Daily injection of human PTH (1-34) to osteoporotics has been shown to increase bone mineral density and reduce fracture risk within 18 months. Despite its impressive effects on human bone, safety became a big issue when it was revealed that up to 53% of rats received hPTH (1-34) for 2 years developed osteosarcoma. On the interpretation of the data, most experts agreed that this is unlikely to predict an increased risk of osteosarcoma in human osteoporotic patients. Some of the reasonings are as follows: (1) fundamental differences in bone metabolism between rat and human, (2) rats received PTH at a dose 12-25 folds of the human dosage, for 80-90% of their life span whereas in human PTH would be used for only 2-3% of the life span.