Risks and causes 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.
Your risk of developing thyroid cancer depends on many factor. These include age and a family history of thyroid cancer.
Anything that can increase your risk of getting a disease is called a risk factor.
Different cancers have different risk factors. Having one or more of these risk factors doesn't mean you will definitely get that cancer.
Age and gender
Thyroid cancer is more common in women than in men during their reproductive years. It peaks in women between the ages of 40 and 44 years. Men are more likely to develop thyroid cancer at an older age. It is most common in men aged between 70 and 74.
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
- surgery to remove your ovaries and/or womb
Being overweight or obese
The risk of thyroid cancer is higher in people who are 
or .
Non cancerous (benign) thyroid disease
Some non cancerous (benign) thyroid conditions increase your risk of thyroid cancer. These include:
- an enlarged thyroid gland (goitre)
- a condition where the immune system attacks the thyroid gland (Hashimoto's disease)
- nodules (adenomas)
Although having a thyroid lump or nodule increases your 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. A close 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.
Speak to your GP if you are concerned about your family history of thyroid cancer.
Inherited faulty genes
Some people have an increased risk of thyroid cancer because of an .
Multiple endocrine neoplasia (MEN)
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 (about 25%) who develop medullary thyroid cancer have an inherited faulty gene associated with MEN.
Familial adenomatous polyposis (FAP)
Familial adenomatous polyposis (FAP) is a bowel condition caused by an inherited gene. Some studies suggest that people with FAP might have an increased risk of thyroid cancer. More research is needed.
Cowden syndrome
You have an increased risk of thyroid cancer if you have Cowden syndrome. Cowden syndrome is a rare inherited disorder. It causes lots of non cancerous (benign) growths called harmatomas. People with this disorder have an increased risk of 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. It is also more common in people who had dental x-rays before 1970. And the risk of thyroid cancer is higher in people who had CT scans of the brain, head and neck when they were children.
Research has looked at people routinely exposed to radiation through their work. This has not shown an increase in their risk of thyroid cancer.
Thyroid cancer may be more common in survivors of atomic explosions or accidents. Thyroid cancer cases rose in the Ukraine after the Chernobyl nuclear reactor accident. Thyroid cancer increased in people exposed when they were children or adolescents.
Some people have low levels of iodine in their body. They might have a higher risk of thyroid cancer after exposure to radiation. This is compared to 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
is an autoimmune condition. Studies suggest that thyroid cancer risk is about 2 times higher in people with this condition.
Having had cancer before
Some studies suggest that people treated as adults for certain cancers have an increased risk of thyroid cancer. These include:
- cancer of the food pipe (oesophageal cancer)
- breast 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.
