What are the risk factors for thyroid cancer?

While the exact cause of most thyroid cancers is not known, several risk factors have been linked to the disease. A risk factor is anything that affects a person’s chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like a person’s age or family history, can’t be changed.

But risk factors don’t tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may have few or no known risk factors. Even if a person with thyroid cancer has a risk factor, it is very hard to know what part that risk factor might have played in the cancer.

Below are some risk factors that make a person more likely to develop thyroid cancer.

Gender and age

Thyroid cancers (like almost all diseases of the thyroid) happen about 3 times more often in women than in men. The reason for this is not known.

Thyroid cancer can occur at any age. But women are most likely to get it in their 40s or 50s, while men are more likely to get it in their 60s or 70s

A diet low in iodine

Follicular thyroid cancers are more common in places where people’s diets are low in iodine. In the United States, most people get enough iodine in their diet because it is added to table salt and other foods.

Radiation

Exposure to radiation is a proven risk factor for thyroid cancer. Sources of such radiation include certain medical treatments and radiation fallout from power plant accidents or nuclear weapons.

Having had radiation treatments to the head or neck in childhood is a risk factor for thyroid cancer. Risk depends on the dose of radiation and the age of the child. Before the 1960s, children were sometimes treated with low doses of radiation for things we wouldn’t use radiation for now, like acne, ringworm, and other problems. Years later, the people who had these treatments were found to have a higher risk of thyroid cancer.

Imaging tests such as x-rays and CT scans also expose children to radiation, but at much lower doses. If there is an increased risk of thyroid cancer from these tests it is likely to be small, but to be safe, children should not have these tests unless they are clearly needed.

Being exposed to radiation as an adult carries much less risk of thyroid cancer.

Hereditary conditions and family history

Several inherited conditions have been linked to different types of thyroid cancer, as has family history. Still, most people who get thyroid cancer do not have an inherited condition or a family history of the disease.

Medullary thyroid cancer

Some cases of medullary thyroid cancer result from a person inheriting an abnormal gene from a parent. This is known as familial medullary thyroid cancer (FMTC). FMTC can occur alone, or it can be seen along with other tumors, as part of a syndrome called multiple endocrine neoplasia type 2 (MEN 2). These cancers often appear in childhood or early adulthood and can spread early.

Other thyroid cancers

People with certain inherited medical problems have a higher risk of more common forms of thyroid cancer. Higher rates of thyroid cancer are seen in people with rare genetic conditions such as:

• Familial adenomatous polyposis (FAP)
• Gardner syndrome
• Cowden disease
• Carney complex, type I

To learn more about these conditions, please see our document, Thyroid Cancer.

Papillary and follicular thyroid cancers also seem to run in some families without known genetic conditions. Having a parent, brother, sister, or child with thyroid cancer increases your risk of thyroid cancer.

If you think you might have an increased risk of thyroid cancer, talk to your doctor. Genetic counseling might be suggested if your background warrants it.