What is thyroid cancer?
Thyroid cancer develops when the cells of the thyroid gland grow and divide in a disorderly (abnormal) way.
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.
Topics on this page:
- How the thyroid gland works
- Thyroid hormones and their role
- What types of thyroid cancer are there?
- What are the risk factors?
- How common is thyroid cancer?
How the thyroid gland works
The thyroid gland is part of the endocrine system, which consists of a group of glands responsible for producing the body’s hormones.
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 calcito
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.
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.
Thyroid hormones and their role
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.
To keep the body working properly, the thyroid gland needs to make 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)
- Not enough thyroid hormone makes your metabolism slow down.
- You may feel tired or depressed, and gain weight easily.
Overactive thyroid (hyperthyroidism)
- Too much thyroid hormone makes your metabolism speed 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.
Having an underactive or overactive thyroid is not typically a sign of thyroid cancer.
What types of thyroid cancer are there?
Common 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
Rare types of thyroid cancer
- about 4% of all thyroid cancers
- develops from the parafollicular cells (C-cells)
- can run 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 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.
- RET 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 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.