Parathyroid carcinoma. Report of three cases.

Primary or relapsing hyperparathyroidism should not be considered a result only of benign conditions like adenoma or hyperplasia (primary or secondary). Parathyroid carcinoma is often the real cause but, because of its rarity, sometimes it is either overlooked or misdiagnosed. Even histologic classification can be erroneous. Distant metastases or ectopic location of the tumors are another potential cause of misdiagnosis, especially when management is decided without the help of diagnostic imaging modalities, particularly those related to the functional aspect of the tumors or their metastases, such as the Tl-201/Tc-99m subtraction scan and the Tl-201 whole body scan.