Thyroid Cancer Risk Factors: 2011 Update

Doctors often cannot explain why one person develops thyroid cancer and another does not. However, it is clear that no one can catch thyroid cancer from another person.

Research has shown that people with certain risk factors are more likely than others to develop thyroid cancer. A risk factor is something that may increase the chance of developing a disease.

Studies have found the following risk factors for thyroid cancer:

• Radiation: 
  
  
  People exposed to high levels of radiation are much more likely than others to develop papillary or follicular thyroid cancer. One important source of radiation exposure is treatment with x-rays. Between the 1920s and the 1950s, doctors used high-dose x-rays to treat children who had enlarged tonsils, acne, and other problems affecting the head and neck. Later, scientists found that some people who had received this kind of treatment developed thyroid cancer.
  
  
  (Routine diagnostic x-rays - such as dental x-rays or chest x-rays - use very low doses of radiation. Their benefits usually outweigh their risks. However, repeated exposure could be harmful, so it's a good idea to talk with your dentist and doctor about the need for each x-ray and to ask about the use of shields to protect other parts of the body.)
  
  
  Another source of radiation is radioactive fallout. This includes fallout from atomic weapons testing (such as the testing in the United States and elsewhere in the world, mainly in the 1950s and 1960s), nuclear power plant accidents (such as the Chornobyl [also called Chernobyl] accident in 1986), and releases from atomic weapons production plants (such as the Hanford facility in Washington state in the late 1940s). 
  
  
  Such radioactive fallout contains radioactive iodine (I-131) and other radioactive elements. People who were exposed to one or more sources of I-131, especially if they were children at the time of their exposure, may have an increased risk of thyroid diseases. For example, children exposed to radioactive iodine from the Chernobyl accident have an increased risk of thyroid cancer.
  
  
  Family history of medullary thyroid cancer: 
• Medullary thyroid cancer sometimes runs in families. A change in a gene called RET can be passed from parent to child. Nearly everyone with the changed RET gene develops medullary thyroid cancer. The disease occurs alone as familial medullary thyroid cancer or with other cancers as multiple endocrine neoplasia (MEN) syndrome.
  
  
  A blood test can detect the changed RET gene. If it's found in a person with medullary thyroid cancer, the doctor may suggest that family members be tested. For those who have the changed gene, the doctor may recommend frequent lab tests or surgery to remove the thyroid before cancer develops.
• Family history of goiters or colon growths: 
• A small number of people with a family history of having goiters (swollen thyroids) with multiple thyroid nodules are at risk for developing papillary thyroid cancer. Also, a small number of people with a family history of having multiple growths on the inside of the colon or rectum (familial polyposis) are at risk for developing papillary thyroid cancer.
• Personal history: 
• People with a goiter or benign thyroid nodules have an increased risk of thyroid cancer.
• Being female: 
• In the United States, women are almost three times more likely than men to develop thyroid cancer.
• Iodine: 
• Iodine is a substance found in shellfish and iodized salt. Scientists are studying iodine as a possible risk factor for thyroid cancer. Too little iodine in the diet may increase the risk of follicular thyroid cancer. However, other studies show that too much iodine in the diet may increase the risk of papillary thyroid cancer. More studies are needed to know whether iodine is a risk factor.

Having one or more risk factors does not mean that a person will get thyroid cancer. Most people who have risk factors never develop cancer.  However it's important to remember that thyroid cancer is the fastest increasing newly diagnosed cancer in America today regardless of age, sex, race or ethnic background.