PTH and osteoporosis: PTH effects on modulating osteoblasts and gene expression has been shown to alter skeletal structure,7, -, 9 and PTH analogs have been used subsequently for treatment of osteoporosis.10 It has also been suggested that PTH may stimulate abnormal osteoblastic activity, and an association between elevated PTH and risk for osteosarcoma formation has been demonstrated in several in vitro11,12 and rat studies.13 Based on these findings in rat models, there have been several human cohort studies6,14,15 evaluating whether there is a relationship between PTH and sarcomas.