Parathyroid carcinoma: update and guidelines for management.

Parathyroid carcinoma is one of the rarest known malignancies that may occur sporadically or as a part of a genetic syndrome. It accounts for approximately 1% of patients with primary hyperparathyroidism. The majority (90%) of parathyroid cancer tumors are hormonally functional and hypersecrete parathyroid hormone (PTH). Thus, most patients exhibit strong symptomatology of hypercalcemia at presentation. Sometimes, it can be difficult to diagnose parathyroid cancer preoperatively due to clinical features shared with benign causes of hyperparathyroidism. Imaging techniques such as neck ultrasound and 99mTc sestamibi scan can help localize disease, but they are not useful in the assessment of malignancy potential. Fine needle aspiration (FNA) prior to initial operation is not recommended due to technical difficulty in differentiating benign and malignant disease on cytology specimens and the possible associated risk of tumor seeding from the needle track. Complete surgical resection with microscopically negative margins is the recommended treatment and offers the best chance of cure. Persistent or recurrent disease occurs in more than 50% of patients with parathyroid carcinoma. Surgical resection is also the primary mode of therapy for recurrence since it can offer significant palliation for the metabolic derangement caused by hyperparathyroidism and allows hypercalcemia to become more medically manageable. However, reoperation is rarely curative and eventual relapse is likely. Chemotherapy and external beam radiation treatments have been generally ineffective in the treatment of parathyroid carcinoma. Typically, these patients require repeated operations that predispose them to accumulated surgical risks with each intervention. In inoperable cases, few palliative treatment options exist, although treatment with calcimimetics can effectively control hypercalcemia in some patients. Most patients ultimately succumb to complications of hypercalcemia rather than from tumor burden or infiltration.