- The thyroid
- What the thyroid gland does
- Thyroid hormones
- What is thyroid cancer?
- Symptoms of thyroid cancer
- Risk factors
- Information reviewed by
The thyroid is a butterfly-shaped gland in the front of the neck. It is found below the voice box (larynx or Adam’s apple) 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 collection of glands responsible for producing the body’s hormones. Hormones are the 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:
- Thyroxine (T4) – 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 to make T4 and T3. Iodine is found in iodised salt, dairy products, seafood and eggs.
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.
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.
- 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
- a rare thyroid cancer (1% of cases)
- usually grows quickly and affects people over 60.
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 90% of 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.
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.
If you have a family history of thyroid cancer, talk to your doctor who may refer you to a genetic counsellor or a family cancer clinic.
Benign thyroid diseases
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.
This website page was last reviewed and updated March 2017.
Information last reviewed January 2016 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.