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Cancer InDepth: Thyroid Cancer

Thyroid cancer is a malignant growth of the cells that make up the thyroid.

The thyroid is an endocrine gland located in the lower neck. It is shaped a bit like a butterfly, with a thin central body (or isthmus) and two “wings” or lobes. Like all endocrine glands, the thyroid produces hormones—chemicals that circulate through the blood to direct functioning in other organs of the body. The thyroid is made up of two types of cells, follicular cells and C cells. The follicular cells produce thyroid hormone, which is involved in regulating body temperature, heart rate, and the body’s use of energy. The C cells produce calcitonin, which is involved in the processing and use of calcium throughout the body.

The Thyroid
The Thyroid
Copyright © Nucleus Medical Media, Inc.

A thyroid tumor grows when cells of the thyroid become cancerous. These cancer cells begin to divide and multiply more quickly than normal cells. Cancer cells also lack the ability to organize themselves in a normal way and have the capability to invade other normal tissue. Growths on the thyroid are often called thyroid nodules. They can be benign (not cancerous) or malignant (cancerous). Luckily, the vast majority (more than 90%) of thyroid nodules are benign.

There are four main types of thyroid cancer:

  • Papillary and follicular thyroid cancer —This type makes up 80%-90% of all thyroid cancers. These are slow-growing cancers of the follicular cells. When caught early and treated, they can be completely cured.
  • Medullary thyroid cancer —This type makes up 5%-10% of all thyroid cancers. This type of cancer affects the thyroid’s C cells and can be treated successfully when caught early, before it has spread (metastasized) to other parts of the body. Medullary thyroid cancer may be hereditary.
  • Anaplastic thyroid cancer —Making up 1%-2% of all thyroid cancer, this type affects the follicular cells, but its cells are highly unusual, fast growing, and very invasive.
  • Hurthle cell cancer —Making up 3% of all thyroid cancer, this type affects thyroid’s follicular cells. Approximately 25% will spread to surrounding lymph nodes in the neck.

Thyroid cancer is the most common type of endocrine gland cancer. About 14,000 cases of thyroid cancer are diagnosed each year, and about 1,100 deaths occur annually due to thyroid cancer. Women are about three times as likely as men to develop thyroid cancer. The average thyroid cancer patient is 45–50 years old when diagnosed.

Causes and Complications

No one knows exactly what causes thyroid cancer. It is clear, however, that certain situations greatly increase a person’s risk of developing the disease. For example, people who have been exposed to radiation (either after nuclear bomb fallout, or through medical use of radiation to the head, neck, chest, or back) have a higher risk of developing thyroid cancer than those who have not. Medullary thyroid cancer also runs in certain families, along with other endocrine cancers. People who have had other conditions affecting their thyroid (chronic goiter, sometimes due to too little iodine in the diet) are also at somewhat greater risk of developing thyroid cancer in the future.

Thyroid cancer can cause an enlarging lump in the neck, hoarseness, difficulty swallowing, and a harsh sound while breathing (called stridor). If thyroid cancer is left untreated, it can spread outside of the thyroid to the nearby lymph nodes, nerves, and blood vessels. It can also spread to distant sites within the body. This is called metastasis. When thyroid cancer spreads, it tends to metastasize to lungs, liver, and bone.

Revision Information

  • Baudin E, Schlumberger M. New therapeutic approaches for metastatic thyroid carcinoma. Lancet Oncol. 2007;8:148-156

  • Conn’s Current Therapy. 54th ed. Philadelphia, PA: WB Saunders Company; 2002: 652-657.

  • Cooper DS, Doherty GM, Haugen BR, et al: The American Thyroid Association Guidelines Taskforce: management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2006;16:1-33

  • Cornett WR, Sharma AK, Day TA et al: Anaplastic thyroid carcinoma: an overview. Curr Oncol Rep. 2007;9:152-158.

  • Rachmiel M, Charron M, Gupta A, et al. Evidence-based review of treatment and follow up of pediatric patients with differentiated thyroid carcinoma. J Pediatr Endocrinol Metab. 2006;19:1377-1393.

  • Thyroid carcinoma. In: Cecil Textbook of Medicine. 21st ed. Philadelphia, PA: WB Saunders Company; 2000: 1247-1250.

  • What is thyroid cancer. American Cancer Society website. Available at http://www.cancer.org/docroot/CRI/CRI%5F2%5F3x.asp?dt=43 . Accessed December 10, 2002.

  • What you need to know about cancer of the thyroid. National Cancer Institute website. Available at http://cancer.gov/ . Accessed December 10, 2002.