Risks and causes of thyroid cancer

A person’s risk of developing thyroid cancer depends on many factors, including age, some non cancerous thyroid conditions and a family history of thyroid cancer. 

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 thyroid cancer.

Age and gender

Thyroid cancer is more common in women than in men, and more so during their reproductive years. The highest number of women diagnosed with thyroid cancer are between the ages of 44 and 49 years. Men are more likely to develop thyroid cancer at an older age. For example between the ages of 80 to 84 years.

The reasons for this are still unclear. Researchers are looking at the relationship between thyroid cancer and:

  • pregnancy
  • the use of oral contraceptives
  • hormone replacement therapy
  • the age periods start
  • the age of menopause

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).

Non cancerous (benign) thyroid disease

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

  • an enlarged thyroid (goitre)
  • a condition where the immune system attacks the thyroid gland (Hashimoto's disease)
  • nodules (adenomas)

It’s important to remember that although having a lump or nodule increases the risk, thyroid cancer is rare. Thyroid lumps are common. But only about 5 out of 100 thyroid lumps (5%) are cancer.

Family history

You have a higher risk of thyroid cancer if a close family member has thyroid cancer. This risk is higher than that of the general population if you have one or more first degree relatives. A first degree relative is a parent, brother, sister, son or daughter. But it’s worth remembering that this risk is still very small because thyroid cancer is rare.

Inherited faulty genes

Some people have an increased risk of developing thyroid cancer because of an inherited change (fault) in a gene Open a glossary item.

For example, some people have changes in the RET gene 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.

MEN2A and MEN2B are rare conditions. Most people found to have MEN are offered surgery to remove their thyroid gland.

About 25 in every 100 people (25%) who develop medullary thyroid cancer have an inherited faulty gene associated with MEN.

Speak to your GP if you are concerned about your family history of thyroid cancer.

Radiation

The thyroid gland is sensitive to radiation. People who have a lot of radiation may develop nodules or lumps on their thyroid some years later.  A lump or nodule on your thyroid doesn’t always mean it is a cancer. But you should always check with your doctor if you find a lump.

Thyroid cancer is more common in people treated with radiotherapy when they were a child. The cancer might develop some years later.

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

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. 

Producing too many hormones

Acromegaly is a rare condition where the body over produces growth hormone. Studies suggest that this may increase the risk of thyroid cancer.

Systemic lupus erythematosus

Systemic lupus erythematosus Open a glossary item is an autoimmune condition. Studies suggest that the risk of thyroid cancer is about 2 times higher in people with systemic lupus erythematosus than the general population.

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.

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: 
25 Mar 2021
Next review due: 
25 Mar 2024
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    L Xu and others 

    Cancer, 2012. 1; 118(5)

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    R Tuttle and others

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    Accessed February 2021

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in if you need additional references for this information.