Causes of thyroid cancer
We do not yet know what causes thyroid cancer in most people, but some things may increase the risk of developing it.
What causes thyroid cancer?
We do not know what causes thyroid cancer in most people. But there are some things that may increase your risk of developing it. These are called risk factors. Having one or more risk factors does not mean you will get thyroid cancer. And if you do not have any risk factors, it does not mean you will not get cancer.
The information here is about papillary and follicular thyroid cancers. Medullary thyroid cancer and anaplastic thyroid cancer have different risk factors.
If you are worried about thyroid cancer and would like to talk to someone, we're here. You can:
- Call the Macmillan Support Line on 0808 808 00 00.
- Chat to our specialists online.
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Benign thyroid disease
Having an overactive or underactive thyroid (hyperthyroidism and hypothyroidism) does not increase your risk of developing thyroid cancer.
But if you have certain types of non-cancerous (benign) thyroid disease, you are slightly more likely to develop thyroid cancer. These include:
- an enlarged thyroid (goitre)
- thyroid nodules (adenomas)
- inflammation of the thyroid (thyroiditis) ¬– including Hashimoto’s thyroiditis.
Benign thyroid disease can run in families. You are more at risk of getting thyroid cancer if you have family members with benign thyroid disease. The risk is higher if more than one family member is affected.
Exposure to radiation
If you have had radiotherapy treatment to the neck area, you have a higher risk of developing thyroid cancer many years later. This risk is higher if you were a child or young adult at the time.
Being exposed to high levels of radiation in the environment can also increase your risk. For example, accidental exposure after a nuclear accident like Chernobyl. This is very rare.
It is important to remember that only a small number of thyroid cancers are caused by any kind of radiation exposure.
Family history
Your risk of developing thyroid cancer is higher if you have a close family member (relative) with thyroid cancer. A close relative is:
- a parent
- a brother or sister (sibling)
- your child.
The risk is still small because thyroid cancer is rare.
Having an inherited altered gene called familial adenomatous polyposis (FAP) can also slightly increase your risk of thyroid cancer. Family members of a person with FAP can have tests to see if they have the same altered gene.
People with PTEN Hamartoma tumour syndrome have a higher risk of thyroid cancer. This is a group of rare conditions which includes Cowden’s syndrome.
Weight
Being overweight may increase the risk of getting thyroid cancer. A healthy diet and regular exercise may reduce the risk.
Sex
Thyroid cancer is more common in women. There may be a link to female hormones.
About our information
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References
Below is a sample of the sources used in our thyroid cancer information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk
British Medical Journal. Best Practice Guidelines, Thyroid cancer. 2020.
European Society Medical Oncology (ESMO): Thyroid cancer, Clinical Practice Guidelines for Diagnosis, Treatment and Follow-up. 2019.
National Institute for Health and Care Excellence (NICE). TA535: Lenvatinib and Sorafenib for treating differentiated thyroid cancer after radioactive iodine. 2018. www.nice.org.uk/guidance/ta535 [accessed May 2021].
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Reviewers
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Professor Nick Reed, Consultant Clinical Oncologist.
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