Thyroid cancer - causes and risk factors
The causes of thyroid cancer in most people are unknown, but research is going on to try to find out more.
There are a number of risk factors that can increase your chance of developing thyroid cancer.
A risk factor is something that increases your chance of developing a health condition such as cancer. For example, smoking is the biggest known risk factor for lung cancer. Having a particular risk factor doesn’t mean you’ll definitely get cancer. However, sometimes people without any known risk factors can develop cancer.
Benign thyroid disease
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People who have certain non-cancerous (benign) thyroid diseases are slightly more likely to develop thyroid cancer. These include:
an enlarged thyroid (goitre)
thyroid nodules (adenomas)
inflammation of the thyroid (thyroiditis).
About 1 in 5 thyroid cancers (20%) occur in people who have had a benign thyroid disease in the past. 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 is affected.
The more common thyroid conditions of an overactive or underactive thyroid (hyperthyroidism and hypothyroidism) don’t increase your risk of developing thyroid cancer.
This may be due to radiotherapy treatment given to the neck area in childhood (for example, enlarged tonsils were treated with radiation before the 1960s). Radiotherapy in childhood to treat a cancer like lymphoma can also increase a person’s risk of developing thyroid cancer many years later. Exposure to high levels of radiation in the environment - for example, in the areas surrounding Chernobyl in the Ukraine following the nuclear power explosion of 1986 - can also increase the risk.
However, only a small number of thyroid cancers are caused by radiation exposure.
In about 1 in 4 people with medullary thyroid cancer, the cancer may be due to an inherited faulty gene called the RET gene.
An inherited gene is a gene that a person is born with, and that is passed down from generation to generation.
The faulty RET gene causes a condition called Multiple Endocrine Neoplasia (MEN) Type 2. There are three types of MEN2:
familial medullary thyroid cancer (FMTC)
multiple endocrine neoplasia (MEN) syndrome type 2A
multiple endocrine neoplasia type 2B.
We have more information in our section about MEN2.
Family members of someone with medullary thyroid cancer can be tested to see if they have inherited an abnormal RET gene.
If they haven’t inherited it they won’t need any monitoring.
If they have, they’ll need to be closely monitored to detect any possible complications at an early stage. Preventative surgery to remove the thyroid gland, before it becomes cancerous, may also be recommended.
There’s a slight increased risk of developing thyroid cancer if you have inherited a faulty gene that causes a bowel condition called familial adenomatous polyposis (FAP). Family members of a person with FAP can be tested to see if they have the same faulty gene.
We have more information in our section about FAP.
It’s thought that people who are overweight may have a higher risk of getting thyroid cancer. A healthy diet and regular exercise may reduce the risk.
We have more information in our sections on healthy eating and cancer, and weight management during and after cancer treatment.