PTH and parathyroid gland adenoma: Conversely to parathyroid adenomas (PAs), parathyroid carcinomas (PCs) show signs of local invasion and/or distant metastases and are characterized by hyperproduction of massive amounts of PTH (up to about 100-fold higher than that of adenomas) and a severe, commonly untreatable, hypercalcemia that accounts for death in a majority of cases.