Parathyroid Cancer

Parathyroid cancer

Definition

Parathyroid cancer is a rare, slow-growing tumor of a parathyroid gland in the neck.

Description

The four parathyroid glands in the human body are designated as the right superior, right inferior, left superior, and left inferior glands. They usually lay adjacent to the thyroid, but rarely can be found in the upper chest. The parathyroid glands secrete parathyroid hormone, which plays a central role in regulating calcium levels in the blood. In the condition called primary hyperparathyroidism, excess production of parathyroid hormone leads to abnormally high levels of calcium (hypercalcemia ). Adenomas, or hyperplasia, of the parathyroid glands are responsible for about 99% of all cases of primary hyper-parathyroidism. Parathyroid cancer accounts for the remaining 1%.

Parathyroid cancer is a slow-growing tumor that manifests itself mainly by production of parathyroid hormone.

Demographics

Only a few hundred cases of parathyroid cancer have been reported in medical literature. It is more common in Japan than in Western countries. No gender preference has been reported. The average age of the patient with parathyroid cancer is in the fifth decade.

Causes and symptoms

Unlike some cancers, there are no predisposing factors that have been found to clearly increase the risk for parathyroid cancer. There are some reported cases of parathyroid cancer arising in patients with adenomas or hyperplasia of the parathyroid.

Most parathyroid cancers are functioning tumors, in that they overproduce parathyroid hormone. Thus, the signs and symptoms of parathyroid cancer are chiefly related to hyperparathyroidism and the resultant hypercalcemia. Common complaints are weakness, fatigue , weight loss , anorexia , constipation, nausea, and vomiting. Patients may also report frequent urination and extreme thirst. Since excess parathyroid hormone causes bones to release too much calcium into the bloodstream, patients may experience bone pain and fractures. The extra calcium in the blood can be deposited in the kidneys, leading to the formation of painful kidney stones. Pancreatitis is another consequence of hypercalcemia. The levels of parathyroid hormone and calcium in patients with parathyroid cancer are usually dramatically elevated— much more so than in patients with benign causes of hyperparathyroidism.

Sometimes the parathyroid cancer is large enough to form a mass in the neck that can be easily felt. If the mass is large enough, it can impinge upon a nerve that controls the vocal cords, leading to hoarseness. In contrast, these features are uncommon in benign hyper-parathyroidism.

Diagnosis

The diagnosis of parathyroid cancer can be difficult because it produces symptoms similar to those of benign hyperparathyroidism due to adenomas or hyperplasia. However, the symptoms of parathyroid cancer are generally more severe and the levels of parathyroid hormone and calcium are usually higher. The presence of a neck mass or hoarseness also suggests cancer. Beyond this, there are no biochemical or radiological tests that can definitively diagnose parathyroid cancer.

There are four general scenarios for the diagnosis of parathyroid cancer:

• Parathyroid cancer is suspected, based on symptoms and signs. Surgery is performed with the intent to remove the cancer.
• A patient with hyperparathyroidism undergoes surgery to remove one or more glands that are thought to contain an adenoma or hyperplasia. During surgery, it is discovered that the underlying lesion is most likely cancer.
• Similarly, a patient with hyperparathyroidism undergoes surgery to remove one or more glands that are thought to contain an adenoma or hyperplasia. After the surgery is complete, the resected specimen is found to contain cancer.
• When symptoms of hyperparathyroidism reappear after surgery, it should raise the suspicion of an incompletely treated parathyroid cancer. This cancer may be localized to the neck or may have spread to distant organs. Several imaging tests can be helpful in this situation. Scintigraphy and ultrasound are useful in detecting recurrent tumors in the neck. Computed tomography (CT scan) and magnetic resonance imaging (MRI) can detect cancer at distant organs, such as the lungs or liver. Sometimes, careful biopsy of a suspected tumor may confirm the diagnosis of cancer.

Clinical staging, treatments, and prognosis

Parathyroid cancer begins in the parathyroid gland and extends to adjacent structures. Late in the course of the disease, it spreads to lymph nodes and ultimately to the lungs and liver.

The best treatment for parathyroid cancer is surgical removal of the cancerous gland. In order to assure complete resection of the cancer, part of the thyroid gland, nearby lymph nodes, and other adherent tissue must be removed with the specimen. Cancer that has spread to distant organs should be removed if possible.

Surgical cure is not possible if the cancer has spread too widely. Therapy then becomes focused on controlling hypercalcemia. General measures include infusing saline solution intravenously to restore lost fluid and to encourage urinary excretion of calcium. Diuretics are drugs that further stimulate urinary excretion of calcium. Bisphosphonates and plicamycin both inhibit the release of calcium from the bone. Other agents, such as gallium nitrate , have shown promise in the treatment of hypercalcemia associated with parathyroid cancer. However, further studies must be conducted to confirm their effectiveness and safety.

The prognosis of parathyroid cancer depends upon the stage of the cancer and the completeness of the surgical resection. If the cancer is detected early and completely removed, cure is possible, but the cancer has been reported to recur up to 20 years after surgery. Cure is unlikely after recurrence. Even so, survival can be signficantly extended by surgery aimed at removing as much recurrent or distant cancer as possible. In general, parathyroid cancer grows and spreads slowly, so that oversecretion of parathyroid hormone is more clinically evident than the actual growth of the cancer.

Alternative and complementary therapies

There have been a few cases in which radiation therapy or chemotherapy have been reported to partially control the growth and symptoms of parathyroid cancer. In the majority of patients, these interventions have not been successful.

Resources

BOOKS

Kinder, Barbara K. "Primary Hyperparathyroidism." In Cur rent Surgical Therapy, 6th ed. Cameron, John L., ed. St Louis: Mosby, 1998, pp.606-12.

Macdonald, John S., D. Haller, I.R. McDougall, et al. "Endocrine System." In Abeloff: Clinical Oncology, 2nd ed. Abeloff, Martin D., ed. New York: Churchill Living stone, 2000, pp.1360-97.

Kevin O. Hwang, M.D.

KEY TERMS

Adenoma

—Benign tumor derived from glandular structures.

Biopsy

—Obtaining a piece of tissue from a living being for diagnostic examination.

Computed tomography

—A radiology test by which images of cross-sectional planes of the body are obtained.

Diuretic

—A drug that promotes the excretion of urine.

Hyperplasia

—Generalized overgrowth of a tissue or organ due to excess number of cells.

Magnetic resonance imaging

—A radiology test that reconstructs images of the body based on magnetic fields.

Pancreatitis

—Inflammation of the pancreas.

Peptic ulcer

—Distinct erosions of the inner layer of the stomach or small intestine.

Scintigraphy

—A radiology test that involves injection and detection of radioactive substances to create images of body parts.

Ultrasound

—A radiology test utilizing high-frequency sound waves.