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What are the risk factors?

The cause of thyroid cancer is unknown, but some factors are known to increase the risk of developing it. Having a risk factor does not necessarily mean that you will develop thyroid cancer. Most people with thyroid cancer have no known risk factors.

A small number of thyroid cancers are due to having radiation therapy to the head and neck area as a child, or living in an area with high levels of radiation, such as the site of a nuclear accident. Thyroid cancer usually takes 10–20 years to develop after significant radiation exposure.

Only around 5% of thyroid cancer runs in families. Having a parent, child or sibling with papillary thyroid cancer may increase your risk. Some  inherited genetic conditions, such as familial adenomatous polyposis or Cowden syndrome, may also increase your risk of developing papillary thyroid cancer.

Most cases of medullary thyroid cancer do not run in families. However, some people inherit a faulty gene called the RET gene. This gene can cause familial medullary thyroid cancer (FMTC) or multiple endocrine neoplasia (MEN).

If you are concerned about having a strong family history of thyroid cancer, talk to your doctor. They may refer you to a genetic counsellor or a family cancer clinic to assess your risk.

People who are overweight or obese possibly have a higher risk of developing thyroid cancer.

Other thyroid conditions, such as thyroid nodules, an enlarged thyroid (known as a goitre) or inflammation of the thyroid (thyroiditis), only slightly increase the chance of developing thyroid cancer.