Thyroid cancer causes and risk factors

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on June 7, 2022.

Approximately 43,000 people a year are diagnosed with thyroid cancer in the United States. Anyone can get thyroid cancer, but some factors may increase a person's risk for developing this disease.

What causes thyroid cancer?

Thyroid cancer forms when the DNA in thyroid cells mutates and grows out of control, forming a tumor.

The specific causes of thyroid cancer in an individual patient may not always be clear. It's important to understand the risk factors that may increase an individual's risk of developing the disease. These factors include hereditary conditions, gender and age.

Thyroid cancer risk factors

Gender and age

Thyroid cancers occur approximately three times more frequently in women than men, although the reason for this difference is unknown. Women also tend to develop these cancers at an earlier age (40s to 50s) than men (60s to 70s).

Is thyroid cancer hereditary?

Certain inherited genetic abnormalities have been linked with the development of different types of thyroid cancer:

  • Inherited mutations in a gene called RET have been associated with the development of medullary thyroid cancers, and account for approximately one out of four cases. This condition is known as familial medullary thyroid cancer (FMTC). If other endocrine glands are also involved, the disease is then called multiple endocrine neoplasia type 2 (MEN 2). Individuals with this genetic mutation often develop FMTC during childhood or early adulthood.
  • It is possible to detect many of the DNA mutations associated with FMTC using a simple blood test and this may be recommended for individuals who have a family history. Genetic counseling can help patients and their families decide if a DNA test is appropriate. Currently, some doctors recommend removing the thyroid gland in individuals who have inherited the RET genetic mutation.
  • Other inherited genetic conditions, such as familial adenomatous polyposis (FAP), Gardner syndrome, Cowden disease and Carney complex type I, are considered risk factors for thyroid cancer, particularly papillary and follicular thyroid cancers.

Even if no known inherited syndrome has been identified, thyroid cancer in a first-degree relative, such as a parent or sibling, raises a person's risk of developing thyroid cancer.

Low-iodine diet

A diet that contains very little iodine has been associated with an increased risk of follicular thyroid cancers. This may explain why these cancers are seen less frequently in the United States, where iodine is added to salt and other foods. Individuals who do not get enough iodine in their diets may also be at increased risk for papillary cancers if they are exposed to radioactivity.

Radiation exposure

Being exposed to radiation, including the kind used for certain medical treatments, as well as fallout from nuclear weapons or power plant accidents, can increase a person’s thyroid cancer risk. In particular, childhood exposure carries a greater risk of later developing thyroid cancer than exposure as an adult.

Conditions and thyroid cancer risk

Other factors that may increase the risk for developing thyroid cancer include being overweight or obese, having an enlarged thyroid or having a history of thyroiditis (thyroid gland inflammation).

Next topic: What are the symptoms of thyroid cancer?

Expert cancer care

is one call away.
appointments in as little as 24 hrs.