PTH and hyperparathyroidism: This was similar to a disease known as hyperparathyroidism, where an increase in parathyroid hormone (PTH) stimulates osteoclastogenesis and bone resorption; however, it was noted that in these patients parathyroid dysfunction was not present, yet immunochemical analyses indicated that there were high levels of a PTH-like protein circulating through the bloodstream, and this “ectopic parathyroidism” was postulated to be secreted by the tumors themselves [5].