Thyroid cancer is a form of cancer that develops from the tissues of the thyroid gland. The thyroid gland is located in the front of the throat, below the thyroid cartilage (also known as the Adam’s apple).
The thyroid gland produces several important hormones, including the thyroid hormone, which is involved in controlling body temperature, weight, energy level and heart rate. The thyroid gland also produces calcitonin, which helps the body use calcium.
The American Cancer Society estimates that over 56,000 people in the United States will be diagnosed with thyroid cancer this year. Compared with other common types of cancer, thyroid cancer occurs more frequently in younger patients. Approximately 80 percent of cases occur in people who are under the age of 65. Women are also approximately three times more likely to develop thyroid cancer than men.
There are several different types of thyroid cancer, which are classified based on how similar they look to normal thyroid cells under a microscope and by the type of cell from which they develop.
Papillary carcinoma is the most common type of thyroid cancer, accounting for approximately 80 percent of cases. Papillary carcinomas are slow growing, differentiated cancers that develop from follicular cells and can develop in one or both lobes of the thyroid gland. This type of cancer may spread to nearby lymph nodes in the neck, but it is generally treatable with a good prognosis (outlook for survival).
Follicular carcinoma is the second most common type of thyroid cancer, and accounts for approximately one out of 10 cases. It is found more frequently in countries with an inadequate dietary intake of iodine. Follicular carcinoma is also a differentiated form of thyroid cancer. In most cases, it is associated with a good prognosis, although it is somewhat more aggressive than papillary cancer. Follicular carcinomas do not usually spread to nearby lymph nodes, but they are more likely than papillary cancers to spread to other organs, like the lungs or the bones.
Hürthle cell carcinoma, also known as oxyphil cell carcinoma, is a subtype of follicular carcinoma, and accounts for approximately 3 percent of all thyroid cancers.
Medullary thyroid carcinoma develops from C cells in the thyroid gland, and is more aggressive and less differentiated than papillary or follicular cancers. Approximately 4 percent of all thyroid cancers will be of the medullary subtype. These cancers are more likely to spread to lymph nodes and other organs, compared with the more differentiated thyroid cancers. They also frequently release high levels calcitonin and carcinoembryonic antigen (CEA), which can be detected by blood tests.
Anaplastic carcinoma is the most undifferentiated type of thyroid cancer, meaning that it looks the least like normal cells of the thyroid gland. As a result, it is a very aggressive form of cancer that quickly spreads to other parts of the neck and body. It occurs in approximately 2 percent of thyroid cancer cases.