Risks for thyroid cancer

Some things can affect your risk, or chance, of developing cancer. Certain behaviours, substances or conditions can increase or decrease the risk. Most cancers are the result of many risks. But sometimes cancer develops in people who don’t have any risks. Exposure to radiation is the main risk for thyroid cancer.

Thyroid cancer can develop at any age, but most cases occur in people 25 to 65 years of age. More women than men develop thyroid cancer. We need more research and can’t say at this time what the risk is for transgender, non-binary and gender-diverse people.

Most of the risks for thyroid cancer can’t be changed. But in some cases, there are things you can do to lower your risk.

The following can increase your risk for thyroid cancer:

Exposure to radiation

Non-cancerous thyroid conditions

Family history of thyroid cancer

Genetic conditions

Excess weight

Tall height

Ionizing radiation is a known risk for cancer. Ionizing radiation is present in the atmosphere. It can also come from medical tests or treatments. The risk of cancer is related to how much radiation you’re exposed to and your age when you’re exposed. Being exposed to radiation when you’re a child carries a higher risk of thyroid cancer compared to exposure that happens when you’re an adult.

If you’ve had radiation therapy to the head or neck, you have a higher risk of developing thyroid cancer many years later. The risk is even higher if you were a child at the time of exposure. The benefit of treating a cancer using radiation therapy usually outweighs the risk of developing thyroid cancer later in life.

In the past, radiation therapy was used to treat health problems such as fungal infections of the scalp, acne or enlarged tonsils in children. Radiation therapy is not used in this way today. Children who received radiation therapy to treat these conditions have an increased risk of developing thyroid cancer.

Being exposed to ionizing radiation from nuclear accidents or weapons increases the risk of developing thyroid cancer. The risk is higher in children who are exposed to the radiation.

Some imaging tests, such as x-rays and CT scans, use ionizing radiation to make images of the body. They use the lowest amount of radiation possible. These tests may increase the risk for thyroid cancer, but we need more research to be sure. The benefits of these tests in helping to diagnose a medical problem usually outweigh the possible risk of cancer.

The following non-cancerous (benign) thyroid conditions increase the risk of thyroid cancer:

• thyroid nodules
• goitre (an enlarged thyroid)
• inflammation of the thyroid (thyroiditis)

Find out more about non-cancerous conditions of the thyroid.

Having a family history of thyroid cancer, especially if your parent, sibling or child has had the disease, increases your risk for thyroid cancer.

A genetic condition is a disease caused by a change (mutation) in one or more genes. If you have a genetic condition that increases your risk for thyroid cancer, you may need to visit your doctor more often. Talk to your doctor about your risk and if you need to have certain tests to check for thyroid cancer.

Having any of these inherited genetic conditions increases your risk of developing thyroid cancer:

Multiple endocrine neoplasia (MEN) is associated with tumours in more than one endocrine gland and an increased risk of developing endocrine system cancers. The thyroid is an endocrine gland. There are different types of MEN, and each type is associated with different cancers. MEN2A and MEN2B increase the risk of tumours in the thyroid (including medullary thyroid cancer), adrenal and parathyroid glands.

Familial adenomatous polyposis (FAP) causes hundreds to thousands of polyps to develop, mainly on the lining of the colon and rectum. People with FAP have a higher risk of developing colorectal cancer and small intestine cancer. It also increases the risk of stomach, adrenal gland and thyroid cancers.

Cowden syndrome is a condition in which many non-cancerous (benign) growths called hamartomas form in the skin, breast, thyroid, colon and intestines and inside the mouth.

Carney complex affects the skin and causes tumours in the heart, endocrine glands (including the thyroid), skin and nerves. Signs include light brown spots on the skin on the face, lips, trunk and mucous membranes.

Werner syndrome causes the body to age very rapidly after puberty. Werner syndrome increases the risk for melanoma, bone, soft tissue and thyroid cancers.

Obesity increases the risk for thyroid cancer.

Learn more about how to have a healthy body weight.

Tall people have a greater risk of developing thyroid cancer, but the reason for this higher risk is not known.

The following have been linked with an increased risk of thyroid cancer, but more research is needed to know for sure that they are risks:

• producing too much growth hormone (acromegaly)
• a diet low in iodine
• higher than normal levels of thyroid-stimulating hormone (TSH)
• reproductive and hormonal factors in women
• diabetes

Significant research shows no link between thyroid cancer and alcohol or smoking.

To make the decisions that are right for you, ask your doctor questions about risks. Learn how cancer can be prevented and what you can do to reduce your risk.