Risk Factors

A risk factor is anything that increases a person’s chance of developing cancer. Some risk factors can be controlled, such as smoking, and some cannot be controlled, such as age and family history. Although risk factors can influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. However, knowing your risk factors and communicating them to your doctor may help you make more informed lifestyle and health-care choices.

The following factors can raise a person’s risk of developing thyroid cancer:

Genetics. Some types of thyroid cancer are associated with genetics.

• An abnormal RET oncogene, which can be passed from parent to child, may cause MTC. Not everyone with an altered RET oncogene will develop cancer. Blood tests and genetic tests can detect the gene. Once the altered RET oncogene is identified, a doctor may recommend surgery to remove the thyroid gland before cancer develops. People with MTC are encouraged to have genetic testing to determine if a mutation of the RET proto-oncogene is present. If so, genetic testing of siblings and children will be recommended.
  
  
• A family history of MTC increases a person’s risk. People with MEN2 syndrome are also at risk for developing other cancers.
  
  
• A family history of goiters increases the risk of developing papillary thyroid cancer.
  
  
• A family history of precancerous polyps in the colon increases the risk of developing papillary thyroid cancer.

Read more about the genetics of thyroid cancer.

Radiation exposure. Exposure to moderate levels of radiation therapy may increase the risk of papillary and follicular thyroid cancers. Such sources of exposure include the following:

• Low-dose to moderate-dose x-ray treatments used before 1950 to treat children with acne, tonsillitis, and other head and neck problems may increase the risk of papillary and follicular thyroid cancers.
  
  
• People who have been treated with radiation therapy for Hodgkin lymphoma or other forms of lymphoma in the head and neck are at an increased risk for developing papillary or follicular thyroid cancer.
  
  
• One or more exposures to radioactive iodine (also called I-131 or RAI), especially in childhood, may increase the risk of papillary and follicular thyroid cancers. Sources of I-131 include radioactive fallout from atomic weapons testing during the 1950s and 1960s, nuclear power plant accidents (for example, the 1986 Chernobyl nuclear power plant accident), and environmental releases from atomic weapon production plants.

Diet low in iodine. Iodine is needed for normal thyroid functioning. In the United States, iodine is added to salt to help prevent thyroid problems.

Gender. Women are two to three times more likely to develop thyroid cancer than men.

Age. Thyroid cancer can occur at any age. Anaplastic thyroid cancer is usually diagnosed after age 60. Older infants (10 months and older) and adolescents can develop MTC, especially if they carry the RET proto-oncogene mutation (see above).

Race. White people are more likely to develop thyroid cancer than black people.