We don’t yet know what causes thyroid cancer in most people. But there are a number of things that may increase your risk of developing it. These are called risk factors. Having a particular risk factor doesn’t mean you will definitely get thyroid cancer. And sometimes people without any known risk factors will develop cancer.
Having an overactive or underactive thyroid (hyperthyroidism and hypothyroidism) does not increase your risk of developing thyroid cancer.
If you have certain types of non-cancerous (benign) thyroid disease, you are slightly more likely to develop thyroid cancer. These types of benign thyroid disease include:
- an enlarged thyroid (goitre)
- thyroid nodules (adenomas)
- inflammation of the thyroid (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 member of your family is affected.
If you have had radiotherapy treatment to the neck area, particularly as a child or young adult, you have a higher risk of developing thyroid cancer many years later.
Exposure to high levels of radiation in the environment can also increase your risk. For example, accidental exposure can happen after a nuclear accident like Chernobyl. But only a small number of thyroid cancers are caused by radiation exposure.
Your risk of developing thyroid cancer is higher if you have a close relative (parent, brother, sister or child) with thyroid cancer. Your risk is still quite small, because thyroid cancer is rare.
There is also a slightly increased risk of developing thyroid cancer if you have inherited an altered gene that causes a bowel condition called familial adenomatous polyposis (FAP). Family members of a person with FAP can have tests to see if they have the same altered gene.