Thyroid Cancer Risk Factors
A family history of thyroid cancer and exposure to radiation are the two risk factors associated with thyroid cancer. Despite this, most people who develop thyroid cancer have no identifiable risk factors at all. About 5% of patients with papillary thyroid cancer will have a family member previously diagnosed with the disease, while about 25% of patients with medullary thyroid cancer will report a family history. Additionally, medullary thyroid cancer can arise within a familial syndrome called multiple endocrine neoplasia type 2 (MEN-2). Patients diagnosed with medullary thyroid cancer should undergo genetic testing to determine if they harbor the gene responsible for this syndrome so that family members can be tested if necessary.
Radiation exposure is also a well-known risk factor for thyroid cancer. Years ago, radiation therapy was used to treat a wide array of ailments including acne, enlarged tonsils, an enlarged thymus, and even ringworm and keloid scars. These applications of radiotherapy have been largely abandoned. However, patients continue to be treated with radiation for certain cancers such as lymphoma, breast and lung cancer.
The radiation exposure from diagnostic x-rays has not been found to be associated with an increased risk of thyroid cancer.
Exposure to high doses of radiation from nuclear bombs and nuclear reactor leaks has also been associated with thyroid cancer. People close to Chernobyl when the meltdown occurred have been followed closely for years. People exposed to the radiation when they were younger than 16 years old at the time have had a significantly increased risk of developing thyroid cancer. It often takes many years for the thyroid cancer to develop following exposure.