Thyroid cancer risks and causes | Cancer Research UK
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Thyroid cancer risks and causes

Men and woman discussing thyroid cancer

This page tells you about the risks and causes of thyroid cancer. You can find the following information


A quick guide to what's on this page

Thyroid cancer risks and causes

Thyroid cancer is quite a rare cancer in the UK. It is 2 to 3 times more common in women than in men.

We don't know what causes all cases of thyroid cancer, but the main risk factors include

  • A history of some types of thyroid disease
  • Exposure to radiation, especially in childhood and having low iodine levels
  • An inherited abnormal gene or a bowel condition called FAP
  • Being overweight
  • A condition where the body overproduces growth hormone (acromegaly)
  • Non cancerous breast conditions

CR PDF Icon You can view and print the quick guides for all the pages in the about thyroid cancer section.



How common thyroid cancer is

Thyroid cancer is quite a rare cancer. Around 2,700 people are diagnosed in the UK each year. Less than 1 in every 100 cancers diagnosed in the UK is a thyroid cancer. It is 2 to 3 times more common in women than in men.

There are different types of thyroid cancer. Papillary thyroid cancer is the most common, followed by follicular thyroid cancer. Medullary tumours and anaplastic tumours are much rarer.

Remember that having a lump in your thyroid does not necessarily mean cancer. Only about 1 in 20 thyroid lumps are cancer.


Definite risk factors

The main risk factors for thyroid cancer are

Benign thyroid disease

Some non cancerous (benign) conditions affecting the thyroid increase your risk, including

  • Nodules (adenomas)
  • An enlarged thyroid (goitre)
  • Inflammation of the thyroid (thyroiditis)

Benign thyroid disease runs in families. If you have this type of condition in your family, then statistically, you have an increased risk of thyroid cancer. The risk is higher if more than one family member is affected.


Thyroid cancer is more common in people who had radiotherapy treatment. The cancer may develop years later – as many as 10 to 40 years after treatment. This risk is highest for people treated with radiotherapy when they were children. But there is a slight increased risk for anyone who has had external beam radiotherapy.

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. And thyroid cancer cases also increased in the USA after nuclear testing in Utah.

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

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

Family history of thyroid cancer

Some people who have family members with thyroid cancer are at a higher risk of developing thyroid cancer themselves. But usually the risk is still small because thyroid cancer is rare. The risk of developing papillary or follicular thyroid cancer is estimated to be 4 to 10 times higher for first degree relatives of a person 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. People who have an inherited gene change (mutation) in a gene called the RET oncogene have an increased risk of medullary thyroid cancer. Some people have gene changes that cause syndromes called MEN2A and MEN2B. MEN stands for multiple endocrine neoplasia. People who have these conditions are more likely to develop medullary thyroid cancer and other cancers of hormone producing glands at some point in their lives. If MEN2 runs in your family, you and your relatives may be referred for screening for thyroid cancer. As many as 1 in 4 people who develop medullary thyroid cancer have an abnormal gene. 

A bowel condition called FAP

People who have a bowel condition called FAP (familial adenomatous polyposis) have an increased risk of thyroid cancer. FAP is another condition caused by an inherited gene. There is detailed information about FAP in the bowel cancer section.

Being very overweight (obese)

Some studies have looked into body weight and thyroid cancer. They 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)

People who have acromegaly have an increased risk of thyroid cancer. Acromegaly is a rare condition where the body over produces growth hormone.


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. 


Possible risk factors

Possible risk factors for thyroid cancer have been suggested by some research reports. But there is no convincing proof yet that they do increase the risk of thyroid cancer. They include

Having had cancer

Some studies show that people treated as adults for non Hodgkin's lymphoma, breast cancer, oesophageal cancer, or testicular cancer have an increased risk of thyroid 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 it is most common in women during their reproductive years. So there have been many studies looking at the relationship between thyroid cancer and reproductive factors and hormone use. 

Researchers have looked at many factors. These include pregnancy history, use of oral contraceptives and hormone replacement therapy, and the age women start their period or go into the menopause. The results of these studies are mixed. Although some studies show there might be a link between these factors and thyroid cancer risk, other studies have not shown a link. 

A very large international study called EPIC hopes to answer questions about diet and cancer. Some researchers looked at information from the women in this study to see if there was a link between thyroid cancer and reproductive and hormonal factors. They concluded that reproductive and hormonal factors do not play a strong role in the development of thyroid cancer. 

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Updated: 27 November 2014