It is possible to develop thyroid cancer with or without the risk factors listed below. However, the more risk factors you have, the greater your chance of having thyroid cancer. If you have a number of risk factors, ask your doctor about steps to take.

Factors that may increase your chances of thyroid cancer include:

• Age —Most common in those aged 40 years or older. Anaplastic thyroid cancer is more common in people aged 60 years or older.
• Gender —Women are more likely to develop thyroid cancer than men. Except for medullary thyroid cancer.
• Environmental and radiation exposure —A history of radiation exposure to the head and neck can increase the risk. This is especially true for children or adolescents. The exposure could be from cancer treatments or repeated CT scans. It can also be the result of radioactive fallout from nuclear accidents or exposures at the World Trade Center site.
• Family history —Thyroid cancers tends to run in families. Risk is higher if a parent or sibling had the cancer.
• Specific genetic mutations —Medullary thyroid cancer is caused by a specific mutation in genes. Mutations are inherited from a parent instead of developing over time. Cancers caused by gene mutations include:
  • Familial medullary thyroid carcinoma
  • RET gene defects, which can cause:
    • Multiple endocrine neoplasia type 2a (MEN2a)—Tumors that affect the adrenal and parathyroid glands
    • Multiple endocrine neoplasia type 2b (MEN2b)—Benign tumor growths on nerve tissue
  • Familial adenomatous polyposis (FAP)—Genetic defect that causes hundreds of colon polyps to develop during adolescence and young adulthood. People with FAP develop colon cancer before the age of 40.
• Medical conditions or syndromes such as:
  • Iodine deficiency (follicular thyroid cancer)—Iodine is needed for thyroid hormone production. Without enough iodine, thyroid tissue grows forming a mass called a goiter. Thyroid masses increase the risk of thyroid cancer. This is not as common in the US because iodine is added to table salt.
  • History of thyroid cancer
  • Obesity, acromegaly, or Sjogren syndrome
  • Organ transplant
• Ethnicity —Thyroid cancer is more common in people of Hawaiian and Polynesian descent.