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Thyroid Cancer (cont.)

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What is thyroid cancer?

Thyroid cancer affects up to 20,000 people in the U.S. every year but accounts for only 1% of new cancers that develop in the U.S. Thyroid cancer is the most common endocrine cancer.

DNA (mutations) that occur spontaneously or in response to an environmental exposure or toxic substances can alter normal thyroid cells. The genetic changes cause the cells to multiply very rapidly without the normal controls found in the rest of the gland. Any of the cell types found in the thyroid gland can mutate into a specific type of cancer.

Cancer is different than goiter, an enlargement of the thyroid gland that may be associated with hyper or hypothyroidism. Worldwide, the most common cause of goiter is iodine deficiency. In countries where table salt is iodinated, the autoimmune disease Hashimoto's thyroiditis, is the most common cause. Graves' disease, another autoimmune disease, can also be associated with thyroid enlargement.

Research from the U.S. National Cancer Institute (NCI) has found that while the number of thyroid cancers being diagnosed has increased in the past 30 years, the death rate from thyroid cancer has remained the same. This suggests that there are not more cancers occurring but instead health care professionals and patients have become better at finding lumps in the thyroid gland and making the diagnosis.

What causes thyroid cancer?

The exact cause of thyroid cancer is not known, though there are factors that may be associated with an increased risk of developing the cancer. Even if the risk factors are present, there is not a way of knowing whether cancer might develop; patients without risk factors still may develop thyroid cancer.

What are the risk factors for thyroid cancer?

Children who have had radiation exposure to the neck are at higher risk for thyroid cancer. Studies have looked at children who were radiated 50 and 60 years ago when the risks of radiation where less well understood, and their rate of thyroid cancer is increased. Children and women survivors of nuclear reactor accidents (Chernobyl in 1986 has been studied) have an increased risk of thyroid and other types of cancer.

X-rays and CT scans of the neck use low doses of radiation but medical testing has not been found to cause thyroid cancer. Nevertheless, in general, it is important to limit the amount of exposures to the least amount of radiation that will provide a clear enough image to help make a diagnosis.

Diets low in iodine may increase the risk of thyroid cancer, but in developed countries, there is usually enough iodine used as food additives that this is not a problem. Lower levels of iodine in the diet may enhance the risk of radiation induced thyroid cancer.

Women are three times more likely to develop thyroid cancer than men and at a slightly younger age (40 to 50 years old for women versus 60 to 70 for men).

There may be a relationship between poorly controlled diabetes and an increased risk of thyroid cancer.

There may be a genetic predisposition to thyroid cancer, especially in certain rare types of thyroid cancer.

While smoking is associated with thyroid disease, worsening hypothyroidism and being a risk factor for Graves' disease, smoking does not appear to increase the risk of thyroid cancer.

Medically Reviewed by a Doctor on 3/24/2017



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