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Risks and causes

Find out what causes thyroid cancer, including non cancerous conditions of the thyroid and radiation.

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.


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 is also 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. The risk is still very small because the cancer is rare.

The risk of developing thyroid cancer is estimated to be 6 to 7 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.

It is possible to inherit abnormal genes that increase your risk of some types of thyroid cancer. For example, some people have gene changes that cause syndromes called MEN2A and MEN2B.  

MEN stands for multiple endocrine neoplasia. People with these syndromes have an increased risk of medullary thyroid cancer. You might be referred for screening for thyroid cancer if MEN2 runs in your family.

About 1 in 4 people (25%) who develop medullary thyroid cancer have an abnormal gene.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is a bowel condition caused by an inherited gene. People with FAP have an increased risk of thyroid cancer.

Being very overweight (obese)

Some studies have found that people who are well above the weight that is normal for their height (obese) have a higher risk of thyroid cancer. 

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.


The risk of thyroid cancer is higher in women with diabetes compared to women who do not have diabetes. This increase in risk is not seen in men who have diabetes. 

Having had cancer

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

  • non Hodgkin's lymphoma
  • breast cancer
  • 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, 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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    Accessed November 2014

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