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 gland
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.
How the thyroid gland works
The thyroid produces three hormones that are released into the bloodstream:
- Thyroxine (T4) – This controls the body’s metabolism. T4 is converted into another hormone called T3.
- Tri-iodothyronine (T3) – Also helps control metabolism. The thyroid produces only small amounts of T3. The majority of this hormone is created when the liver and kidney convert T4 into T3. The active form of the thyroid hormone is T3.
- Calcitonin – This hormone has a small role in controlling the body’s calcium levels.
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:
- follicular cells – make a protein called thyroglobulin (Tg) and produce and store T4 and T3
- parafollicular cells (C-cells) – produce calcitonin.
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):
- Underactive thyroid (hypothyroidism) – When there is not enough thyroid hormone, your metabolism slows down. You may feel tired or depressed, and gain weight easily.
- Overactive thyroid (hyperthyroidism) – When there is too much thyroid hormone, your metabolism speeds up. You may lose weight, have an increased appetite, feel shaky and anxious, or have rapid, strong heartbeats (palpitations). Over time, untreated hyperthyroidism can result in loss of bone strength and problems with heart rhythm.
What is thyroid cancer?
Thyroid cancer develops when the cells of the thyroid gland grow and divide in a disorderly (abnormal) way.
What types are there?
There are several types of thyroid cancer.
- most common type (about 70–80% of all cases)
- develops from the follicular cells
- tends to grow slowly
- about 20% of thyroid cancer cases
- develops from the follicular cells
- includes Hürthle cell carcinoma, a less common subtype
- about 4% of all thyroid cancers
- develops from the parafollicular cells (C-cells)
- can run in families in families
- a rare thyroid cancer (1% of cases)
- may develop from papillary or follicular thyroid cancer
- usually grows quickly, and affects people over 60
What are the signs and symptoms?
Thyroid cancer usually develops slowly, without many obvious signs or symptoms. However, some people experience one or more of the following:
- a painless lump in the neck or throat, which may gradually get bigger
- trouble swallowing
- difficulty breathing
- a hoarse voice
- swollen lymph glands in the neck, which may slowly grow in size over months or years.
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.
When to see a doctor
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.
What are the risk factors?
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.
Exposure to radiation
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.
How common is 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.
- The thyroid gland is at the front of the neck below the voice box (larynx). It produces hormones that help control the body’s heart rate, blood pressure, body temperature and weight.
- These hormones are called thyroxine (T4), tri-iodothyronine (T3) and calcitonin.
- Thyroid cancer develops when the cells of the thyroid gland grow and divide in an abnormal way.
- There are four main types of thyroid cancer. The most common type is papillary thyroid cancer – it affects 70–80% of people diagnosed with thyroid cancer.
- Thyroid cancer often develops slowly, without obvious signs or symptoms. However, the most common sign is a painless lump in the neck. This is also called a nodule.
- In most cases, a thyroid nodule is a symptom of a goitre. This is when the thyroid becomes enlarged, and it is a benign condition (not cancer).
- An underactive thyroid (hypothyroidism) or overactive thyroid (hyperthyroidism) isn’t usually a sign of thyroid cancer.
- The exact cause of thyroid cancer is unknown, but exposure to radiation either in the environment or due to radiation in childhood, or family history may increase the chance of developing thyroid cancer.
- About 2100 people are diagnosed with thyroid cancer each year in Australia. It’s three times more common in women than men.
Reviewed by: A/Prof Julie Miller, Specialist Endocrine Surgeon, The Royal Melbourne Hospital, Epworth Freemasons and Melbourne Private Hospitals, VIC; Polly Baldwin, Cancer Council Nurse, 13 11 20, Cancer Council SA; Dr Gabrielle Cehic, Nuclear Medicine Physician, Flinders Medical Centre, Lyell McEwin Hospital and The Queen Elizabeth Hospital, SA; Dr Kiernan Hughes, Endocrinologist, San Clinic Specialist Rooms & Chatswood Rooms, Northern Endocrine Pty Ltd, NSW; Dr Chris Pyke, A/Prof of Surgery, University of Queensland, Mater Hospital, Brisbane, QLD; and Jen Young, Consumer.