Abstract

Introduction: Parathyroid carcinoma (PC) is a rare disease that causes extreme hypercalcemia. It accounts for less than 1% of primary hyperparathyroidism (PHPT), and the symptoms are caused by hypercalcemia secondary to excess parathyroid hormone (PTH) production from the tumor. Calcium and PTH tend to be higher or show an extreme level (total calcium >14 mg/dL), but the range could overlap with PHPT. There is no specific sign or diagnostic test to differentiate PC from benign causes of PHPT. Therefore, the diagnosis of PC is made by pathologic diagnosis after surgery. Surgery with en bloc resection offers the best chance for cure; thus, it is essential for surgeons treating hyperparathyroidism to know the predisposing factors and clinical features of PC and to perform adequate resection at the first surgery. Other adjuvant therapies, such as chemotherapy or radiotherapy, rarely result in long-term cures for the disease. PCs are indolent tumors, and the risk of recurrence or metastasis persists throughout the patient's lifetime. Death from PC usually results from uncontrollable hypercalcemia rather than tumor burden. This comprehensive chapter will focus on diagnostic suspicion and therapeutic options, including their limitations in treating PC.