Parathyroid cancer is extremely rare (almost 1 in 2 million). Cases of parathyroid cancer make up less than 1% of the total number of patients with primary hyperparathyroidism. Patients are usually older than 30, and it affects men and women equally. Patients with parathyroid cancer typically have a very high calcium level (greater than 14 mg/dL) and a very high parathyroid hormone (PTH) level (greater than five times the upper limit of normal, usually greater than 300 pg/mL or more). About half of patients with parathyroid cancer will present with a hard mass in the neck. The pathologist may not be able to tell if this is cancer even by looking at it under the microscope. Parathyroid cancer is a clinical diagnosis, meaning that you make the diagnosis of parathyroid cancer by the patient’s symptoms, blood tests, and findings in the operating room.
The best chance of curing parathyroid cancer is to catch the disease early and remove it promptly. By the time it is diagnosed, parathyroid cancer may have grown into surrounding structures like the thyroid. One third of patients will have lymph node metastases upon presentation and one third will have distant metastases. The best treatment for parathyroid cancer is an operation to remove the parathyroid cancer along with the thyroid lobe on that same side and any other involved tissue.
The risks for this operation are similar to that for other parathyroid operations (see Risks of Parathyroid Surgery). After the operation, your surgeon will follow you with routine calcium and PTH levels to see if the cancer comes back (recurs). In addition, you will likely have imaging tests like an ultrasound of the neck or PET scan (special radiology test looking for cancer). If the cancer comes back, you may need another operation to remove more of the disease (See Special Cases: Re-operative Parathyroid Surgery). Chemotherapy and radiation therapy do not work well against parathyroid cancer. Fortunately, parathyroid cancer is often slow growing and patients can have repeat operations to remove disease as it comes back.
Of course, each operation raises the risk for a subsequent operation. Hypercalcemia is the primary cause of morbidity and mortality in parathyroid carcinoma patients. For patients who are not eligible for an operation, other treatments like medications that lower the calcium levels (e.g., calcimimetics, bisphosphonates, denosumab) can help improve the symptoms and prolong life (see Alternatives to Surgery).