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Risks and causes

Find out what increases the risk of developing thyroid cancer, including radiation and some types of non cancerous thyroid conditions.

We don’t know what causes most thyroid cancers. But there are some factors that might increase your risk of developing it.

Having any of these risk factors doesn’t mean that you will definitely develop cancer.

Benign thyroid disease

Some non cancerous (benign) conditions of the thyroid increase your risk of thyroid cancer. These include:

  • nodules (adenomas)
  • an enlarged thyroid (goitre)
  • inflammation of the thyroid (thyroiditis)

You have an increased risk if you have one of these conditions in your family. The risk is higher if more than one family member is affected.

Radiation

Thyroid cancer is more common in people who had radiotherapy treatment, particularly in people treated with radiotherapy when they were children. The cancer might develop some years later.

Thyroid cancer may be more common in survivors of atomic explosions or accidents. After the Chernobyl nuclear reactor accident, cases of thyroid cancer in the Ukraine rose in people exposed to radiation, particularly as children or adolescents. 

People who have low levels of iodine in their body might have a higher risk of thyroid cancer after exposure to radiation than people with normal iodine levels. 

Research has shown that the risk of thyroid cancer is not increased in people routinely exposed to radiation through their work. 

Family history

You have a higher risk if you have a family member with thyroid cancer. But the risk is still very small because the cancer is rare.

The risk of developing thyroid cancer is estimated to be 4 times higher for people with a first degree relative with thyroid cancer, than people in the general population. A first degree relative is a parent, brother, sister, son or daughter.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is a bowel condition caused by an inherited gene. Some studies have suggested that people with FAP might have an increased risk of thyroid cancer. But more evidence is needed. 

Being very overweight (obese)

The risk of thyroid cancer is higher in people who are overweight or obese (have a higher weight than is normal for their height).

Producing too much growth hormone (acromegaly)

Acromegaly is a rare condition where the body over produces growth hormone. This increases the risk of thyroid cancer.

Diabetes

Some studies suggest that the risk of thyroid cancer may be higher in women with diabetes compared to women who do not have diabetes. But the evidence is mixed.

An increase in risk is not seen in men who have diabetes. 

Having had cancer before

Some studies suggest that people treated as adults for certain cancers have an increased risk of thyroid cancer. These include:

  • non Hodgkin lymphoma
  • breast cancer
  • cancer of the food pipe (oesophageal cancer)
  • testicular cancer

It is not known if this is due to treatment for these cancers, common risk factors or inherited genetic changes. In the case of oesophageal cancer, it may be because routine checks after treatment pick up the thyroid cancers.

Factors related to women and reproduction

Thyroid cancer is more common in women than in men, and more so during their reproductive years. Researchers have looked at the relationship between thyroid cancer and:

  • pregnancy history
  • use of oral contraceptives
  • hormone replacement therapy
  • age period starts
  • age of menopause

The results of these studies are mixed. Some studies show there might be a link with some factors, but others don’t. 

Reducing your risk and other possible causes

You might have heard of other possible causes of cancer. Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence.

We haven’t included them here, either because there is no evidence about them or it is less clear.

Last reviewed: 
27 Nov 2014
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