Overview

Thyroid cancer begins in the thyroid gland, which is located in the front of the neck just below the larynx (voice box). The thyroid gland is part of the endocrine system, which regulates hormones in the body. The thyroid gland absorbs iodine from the bloodstream to produce thyroid hormone, which regulates a person’s metabolism.

Thyroid cancer begins when the cells in the thyroid begin to change, grow uncontrollably, and eventually form a tumor. There are two types of tumors: benign (noncancerous) and malignant (cancerous, meaning that it can spread to other parts of the body). Thyroid tumors can also be called nodules, and 90% of all thyroid nodules are benign.

A healthy thyroid gland is barely palpable (capable of being touched or felt). A normal gland has two lobes, one on each side of the windpipe, joined by a narrow strip of tissue called the isthmus. If a tumor develops in the thyroid, it is felt as a lump in the neck. A swollen or enlarged thyroid gland is called a goiter, which may be due to iodine deficiency. Most Americans receive enough iodine from salt, and a goiter under these circumstances is caused by other reasons.

The thyroid gland contains two types of cells: follicular cells, which are responsible for the production of thyroid hormone, and C cells, which make calcitonin, a hormone that participates in calcium metabolism.

There are four main types of thyroid cancer:

Papillary thyroid cancer. Papillary thyroid cancer develops from the follicular cells and grows slowly. It is usually found in one lobe; only 10% to 20% of papillary thyroid cancers appear in both lobes. Papillary thyroid cancer is a differentiated thyroid cancer, meaning that the tumor looks similar to normal thyroid tissue under a microscope.

Follicular thyroid cancer. Follicular thyroid cancer also develops from the follicular cells and usually grows slowly. Follicular thyroid cancer is also a differentiated thyroid cancer, but it is less common that papillary thyroid cancer.

These two types of cancer are very often curable, especially when found early and in people younger than 45. Together, papillary and follicular thyroid cancers make up 80% to 90% of thyroid cancers.

Medullary thyroid cancer (MTC). MTC develops in the C cells and is sometimes the result of a genetic syndrome called multiple endocrine neoplasia type 2 (MEN2). This tumor has very little, if any, similarity to normal thyroid tissue. MTC can often be controlled if it is diagnosed and treated before it spreads to other parts of the body. MTC accounts for 5% to 10% of thyroid cancers.

Anaplastic thyroid cancer. This rare and fast-growing, poorly differentiated thyroid cancer starts from differentiated thyroid cancer or a benign tumor of the gland. Anaplastic thyroid cancer can be subtyped into giant cell classifications. Because this type of cancer grows so quickly, it can be more difficult to treat successfully.

This section addresses these four main types of thyroid cancer. For lymphoma in the thyroid, please read Cancer.Net’s Guide to Lymphoma, Non-Hodgkin. For more information on sarcoma in the thyroid, review the Guide to Sarcoma. For information on a tumor in the parathyroid gland, read Cancer.Net’s Guide to Parathyroid Cancer.

Statistics

In 2009, an estimated 37,200 adults (10,000 men and 27,200 women) in the United States will be diagnosed with thyroid cancer. It is estimated that 1,630 deaths (690 men and 940 women) from this disease will occur this year. Thyroid cancer is the seventh most common cancer in women.

The five-year relative survival rate (the percentage of people who survive at least five years after the cancer is detected, excluding those who die from other diseases) for all stages of thyroid cancer is about 97%. The five-year relative survival rate of papillary and follicular thyroid cancers and MTC range from 97% to 100% for early-stage cancer and decrease with later-stage cancer (See Staging). Anaplastic thyroid cancer is associated with a much lower survival rate.

Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States each year, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with thyroid cancer. Because the survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.

Statistics adapted from the American Cancer Society’s publication, Cancer Facts & Figures 2009.

Find out more about basic cancer terms used in this section.