Thyroid Cancer Risk Factors
Age and Sex: Patients with thyroid cancer are more likely to be female (three times more likely than males) and over 45 years of age. Anaplastic thyroid cancer almost always occurs in patients over 60. In evaluating whether a thyroid nodule may be malignant, a malignant nodule is much more likely if the patient is male and under the age of 20.

Race: Caucasians are more likely than African-Americans to develop thyroid cancer.

Childbearing Age: Women who have their last pregnancy after age 30 are at higher risk.

Previous goiter/benign thyroid nodule

Family history of medullary thyroid cancer (either FMTC or the MEN syndromes)

Family history of multinodular goiter

Family history of colon growths (Gardner’s syndrome/familial adenomatous polyposis, or FAP)

Having Cowden’s disease (a rare inherited disorder)

Iodine deficiency or excessive iodine intake

Radiation exposure - this can be from prior radiotherapy treatment for other forms of cancer, exposure to atomic testing or nuclear power plant accidents or other occupational exposure. In addition, doctors used to routinely administer X-ray treatment to the head and neck area for conditions such as acne, fungal infections of the scalp and enlarged tonsils. This also was a significant cause of unnecessary radiation exposure.