On this page: The thyroid gland | Thyroid hormones | What is thyroid cancer? | What types are there? | What are the signs and symptoms? | What are the risk factors? | How common is thyroid cancer? | Key points
The thyroid is a butterfly-shaped gland at the front of the neck. It is found below the voice box (larynx) and is made up of two halves, called lobes, which lie on either side of the windpipe (trachea). The lobes are connected in the middle by a small band of thyroid tissue known as the isthmus.
The thyroid gland is part of the endocrine system, which consists of a group of glands responsible for producing the body’s hormones. Hormones are chemical messengers that help the body function properly. The thyroid gland makes hormones that control the speed of the body’s processes, such as heart rate, blood pressure, body temperature and weight – this is known as your metabolic rate.
The thyroid produces three hormones that are released into the bloodstream:
The thyroid gland needs iodine – found in foods such as seafood, iodised table salt, some dairy products, soy beans and soy-containing products, and eggs – to make T4 and T3.
The thyroid gland is made up of two main types of cells:
Behind the thyroid glands are four parathyroid glands. These glands produce a hormone called parathyroid hormone or PTH, which controls the amount of calcium in the blood.
To keep the body working properly, it is important that the thyroid gland makes the right amount of thyroid hormone.
The pituitary gland, located at the base of the brain, controls the release of thyroid hormone from the thyroid gland.
If thyroid hormone (T3 and T4) levels drop below normal, the pituitary gland produces a hormone called thyroid-stimulating hormone (TSH) to prompt the thyroid gland to make and release more T3 and T4. Too much T3 and T4 lowers, or suppresses TSH production by the pituitary gland.
Changes in thyroid hormone levels can affect how your cells respond (metabolism):
Thyroid cancer develops when the cells of the thyroid gland grow and divide in a disorderly (abnormal) way.
There are several types of thyroid cancer.
Thyroid cancer usually develops slowly, without many obvious signs or symptoms. However, some people experience one or more of the following:
Having a painless lump in the neck is the most common sign. However, thyroid lumps, known as nodules, are relatively common and most are benign. In about 9 out of 10 cases, a thyroid nodule is a symptom of a goitre (a benign enlarged thyroid gland) or another condition affecting the head or neck.
If you notice any of these symptoms, you should see your general practitioner (GP) as soon as possible.
The earlier a cancer is picked up, the easier it is to treat and the more successful treatment is likely to be.
Having an underactive or overactive thyroid (hypothyroidism or hyperthyroidism) is not typically a sign of thyroid cancer.
The exact cause of thyroid cancer is unknown, but several factors are known to increase the risk of developing it. Having some of these risk factors 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 cancer cases are due to having radiotherapy to the head and neck area as a child, or living in an area with high levels of radiation in the environment, such as a nuclear accident site. Thyroid cancer usually takes 10–20 years to develop after radiation exposure.
Some people inherit a faulty gene called the RET gene, which increases their risk of developing thyroid cancer. This gene can cause familial medullary thyroid cancer (FMTC) or multiple endocrine neoplasia (MEN).
Having a first-degree relative (parent, child or sibling) with papillary thyroid cancer may also increase your risk.
If you have a family history of thyroid cancer, ask your doctor to refer you to a genetic counsellor or a family cancer clinic.
Having a thyroid condition, such as thyroid nodules, an enlarged thyroid (goitre) or inflammation of the thyroid, only slightly increases your chance of developing thyroid cancer.
About 2100 people are diagnosed with thyroid cancer each year in Australia. Thyroid cancer occurs three times more often in women than men – it is the seventh most common cancer affecting Australian women.
The average age of a woman diagnosed with thyroid cancer is 51; the average age for a man to be diagnosed with thyroid cancer is 54.
Thyroid cancer cases have increased in recent years. Between 1982 and 2014, cases of thyroid cancer increased by 281%. Researchers are trying to determine the cause of this increase. One contributing factor is improved imaging quality that can detect smaller cancers during ultrasounds and other scans performed of the area for other reasons.