The thyroid gland
The thyroid is a small gland in the front of the neck just below the voicebox (larynx). It is made up of two parts, or lobes, and is part of the endocrine system. This system makes the body’s hormones that help to control and influence various functions.
The thyroid is sometimes known as the ‘activity’ gland because it produces the two main hormones thyroxine (T4) and triiodothyronine (T3). These keep the body functioning at its normal rate. The thyroid gland needs a regular supply of iodine, which is found in fish, seafood and dairy products, to produce thyroid hormones. We take in iodine from our diet.
The thyroid gland
If the levels of T3 and T4 in the blood fall, a part of the brain called the hypothalamus senses this. It responds by sending out thyroid-releasing hormones (TRH) into the blood. As the level of TRH in the blood rises, it activates another gland in the brain called the pituitary gland to release thyroid-stimulating hormones (TSH). TSH stimulates the thyroid to produce more T3 and T4 thyroid hormones.
If the thyroid gland doesn’t produce enough hormones, you’ll feel tired and lethargic and put on weight easily.
This is called hypothyroidism or myxoedema. If the thyroid gland produces too many hormones, it’s called hyperthyroidism or thyrotoxicosis. You’ll lose weight, feel hungrier than normal, and shaky and anxious.
Your heartbeat may also be faster than normal or irregular.
Thyroid cancer is uncommon.
It’s more common in women than men, and most women who have thyroid cancer are diagnosed between the ages of 35 and 39. Thyroid cancer in men is more likely to occur above the age of 70. It is rare in children.
There are different types of thyroid cancer, which are divided into four different groups. This is because of the way the thyroid cells look when examined under a microscope.
Types of thyroid cancer
This is the most common type of thyroid cancer. It’s slow-growing and is found more in younger people, mostly women.
This is a less common type of cancer, usually found in young or middle-aged people. Papillary and follicular thyroid cancers are sometimes grouped together under the name differentiated thyroid cancer (DTC), as they are often treated in the same way. Most differentiated thyroid cancers are cured.
This is a rare type of thyroid cancer that can run in families. For this reason, members of your family may be checked to see if they are also at risk of developing this cancer.
This is a rare type of thyroid cancer that is fast-growing. It’s more common in people over 60 and in women. Unlike other types of thyroid cancer, it can be very difficult to treat.
It’s also possible to have a lymphoma of the thyroid gland. This starts in the lymph tissue of the thyroid. The lymph tissue is part of the body’s lymphatic system. Most thyroid lymphomas are a type of non-Hodgkin lymphoma (NHL).
We have more information in our section on thyroid lymphoma.
Your doctor will be able to tell which type of thyroid cancer you have by examining a sample of cells from the cancer. Apart from the anaplastic and lymphoma types, thyroid cancer tends to develop very slowly, and it may be some years before it starts to cause any problems. With treatment, the outlook for most people with thyroid cancer is very good and most people are cured, even if the cancer has spread beyond the thyroid.
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
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.
Exposure to radiation
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.
Inherited faulty gene
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.
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.