In recent years, scientists have learned a great deal about the changes that happen in the cells of the thyroid when cancer develops. They have learned, for example, that certain changes in the DNA (a chemical that carries the instructions for nearly everything our cells do) can make normal cells cancerous.
Changes (mutations) in certain genes seem to be involved in the development of some forms of papillary thyroid and follicular thyroid cancers. In most cases, mutations in the genes that control the growth and division of cells that are related to thyroid cancer occur after you are born and are not inherited from your parents. Sometimes these mutations are caused by exposure to radiation; radiation therapy was often used to shrink enlarged tonsils or adenoids and treat skin problems (such as acne) in children. However, certain mutations in the RET gene that can cause medullary thyroid carcinoma are inherited from your parents.
Risk Factors for Thyroid Cancer
Doctors and researchers believe that certain factors, known as risk factors, increase a person’s chances of getting thyroid cancer. However, not everyone with a risk factor will develop thyroid cancer and people without any risk factors can develop the disease.
Risk factors for thyroid cancer include:
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Age - Most cases of papillary and follicular thyroid cancer are found in people between the ages of 20 and 60 years. However, benign thyroid nodules and thyroid cancers can occur in people of all ages.
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Diet - Follicular thyroid cancers are more common in parts of the world where people's diets are low in iodine. In the United States, people have plenty of iodine in their diets because iodine is added to table salt and other food. A diet low in iodine may also increase the rate of papillary cancer if you have been exposed to radiation.
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Exposure to radiation - A history of head or neck radiation treatments in childhood is a proven risk factor for papillary and follicular thyroid cancer. Children used to be treated with x-rays for acne, fungus infections of the scalp, an enlarged thymus gland, or problems with their tonsils or adenoids. People who were treated with radiation as children for cancer also have a higher risk of thyroid cancer.
Radioactive fallout, including fallout from atomic weapons testing and nuclear power plant accidents (such as the one at Chernobyl in 1986) is another source of radiation. This radioactive fallout contains radioactive iodine (I-131). People who were exposed to I-131, especially if they were children at the time, may have an increased risk for thyroid diseases.
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Family history - About 20 percent of medullary thyroid carcinomas (MTCs) happen in people who have inherited an abnormal gene from their parents. If this abnormal gene runs in your family, then you may be at very high risk of developing MTC and you should ask your doctor for information about blood chemistry tests and genetic testing. People with certain inherited medical conditions, including Gardner's syndrome and familial polyposis (genetic disorders in which large numbers of precancerous polyps develop throughout your colon and upper intestine), are also at higher risk of papillary thyroid cancer. Cowden disease, a rare, inherited disorder that causes lesions on your face, hands, and feet, and inside your mouth, also increases your risk of developing thyroid cancer and breast cancer.
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Gender - Benign thyroid nodules and thyroid cancers occur almost three times more often in women than in men.
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Race - White people in the United States are more likely than African Americans to be diagnosed with thyroid cancer.
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Reproductive history - Women whose last pregnancy occurs at age 30 or later have a higher risk of thyroid cancer than women who have children earlier in life.
This content has been reviewed and approved by Myo Thant, MD.