Clonal malignant cells originating in the parenchyma of the inferior parathyroid glands. Uncommonly in the mediastinum. Onset of parathyroid carcinoma may be related to excessive parathyroid hormone production, leading to primary hyperparathyroidism. Characterized by greatly elevated parathyroid hormone (PTH) and moderate to severe hypercalcemia. Often presenting with a neck mass. Other signs and symptoms include bone pain, dysphagia, dysphonia, muscle weakness, nausea, and vomiting.

Pathologic confirmation of capsular, perineural, or blood vessel invasion of parathyroid adjacent structures or distant metastases can distinguish malignancy from benign adenoma. Untreated, parathyroid gland carcinoma has a poor prognosis. The likely cause of death is due to complications caused by hypercalcemia.

Management includes surgical "en bloc" resection of ipsilateral lobe and involved tissue. More severe malignancy calls for comprehensive resection. Radiation therapy has mixed reviews. Chemotherapy has not garnered positive results; however, treatment of hypercalcemia by pharmacotherapies can provide temporary relief of symptoms. Calcimimetics (to decrease PTH production) may reduce complications and extend survival time.