About thyroid cancer

Thyroid cancer develops when the cells of the thyroid grow and divide in an abnormal way. There are several types of thyroid cancer. It’s rare but possible to have more than one type at once. Thyroid nodules called adenomas are not cancer (benign).

Learn more about:

• The thyroid
• The role of thyroid hormones
• Types of thyroid cancer
• What causes thyroid cancer?
• What are the risk factors?
• Who gets thyroid cancer?

The thyroid 

The thyroid is a butterfly-shaped gland that sits at the front of the throat. It has two halves, called lobes, that are connected by a small band of thyroid tissue called the isthmus. These two lobes sit on either side of the windpipe (trachea), just below the voice box (larynx).

The role of the thyroid

The thyroid is part of the endocrine system. This system is made up of glands that make hormones, which are chemical messengers that help the body function.

The thyroid makes hormones that control your metabolic rate, including your heart rate, how fast you digest food, your body temperature and weight. These hormones are called T4 and T3.

The thyroid also makes a hormone called calcitonin, which helps to control calcium levels in your bloodstream. See more information below about the role of these hormones.

Cells in the thyroid

There are 2 main types of cells in the thyroid:

• follicular cells – produce and store the hormones T4 and T3, and make a protein called thyroglobulin (Tg)
• parafollicular cells (C-cells) – produce the hormone calcitonin.

Parathyroid glands

Behind the thyroid are 4 small glands known as the parathyroid glands. They make parathyroid hormone (PTH), which works with calcitonin to control the amount of calcium in the bloodstream.

The thyroid

 Front view

Rear view

The role of thyroid hormones

The hormones T4 (thyroxine) and T3 (tri-iodothyronine) are known as the thyroid hormones. To make these hormones, the thyroid needs iodine, which is found in foods such as seafood and iodised salt.

T4 is the main hormone that is made by the thyroid, but it is converted by the liver and kidneys into T3, a much more powerful hormone. Most of your T3 is created when the liver and kidneys convert T4 into T3, but the thyroid also makes small amounts.

To keep the body’s metabolism working properly, it is important that the thyroid makes the right amounts of T4 and T3. This balance of hormones is controlled by the pituitary gland, which is located at the base of the brain:

• If the levels of T4 and T3 drop below normal, the pituitary gland produces more of a hormone called thyroid-stimulating hormone (TSH). TSH causes the thyroid to make and release more T4 and T3.
• If the levels of T4 and T3 are too high, the pituitary gland produces less TSH.

Changes in thyroid hormone levels affect your metabolism by slowing down or speeding up the body’s processes, as outlined below.

Underactive thyroid (hypothyroidism) – If you don’t have enough thyroid hormones, your metabolism slows down. As a result, you may feel tired or depressed, and gain weight easily.

Other symptoms may include:

• difficulty concentrating
• constipation
• brittle and dry hair and skin
• sluggishness and fatigue
• in severe cases, heart problems could occur.

Overactive thyroid (hyperthyroidism) – If you have too many thyroid hormones, your metabolism speeds up. As a result, you may:

• lose weight
• have increased appetite
• feel shaky and anxious
• have rapid, strong heartbeats (palpitations).

Over time, untreated hyperthyroidism can result in loss of bone strength and problems with heart rhythm and heart function.

Types of thyroid cancer

Common types:

Rare types:

What causes thyroid cancer?

What exactly causes thyroid cancer is unknown, but some things may increase your risk of developing it. Having one of these risk factors does not mean that you will develop thyroid cancer.

What are the risk factors?

Exposure to radiation

A small number of thyroid cancers may be from having radiation therapy to the head and neck as a child, living in an area with high levels of radiation, or from exposure to radiation at work (e.g. medical or military). Thyroid cancer usually takes 10–20 years to develop after significant radiation exposure.

Family history

A small number of thyroid cancers (about 5%) are linked to a family history. These include:

• Papillary thyroid cancers – Having a parent, child or sibling with papillary thyroid cancer or an inherited genetic condition, such as familial adenomatous polyposis (FAP) or Cowden syndrome, may increase your risk.
• Medullary thyroid cancers – Some people inherit a faulty gene, called the RET gene, that can cause familial medullary thyroid cancer (FMTC) or multiple endocrine neoplasia (MEN).

If you have a family history of thyroid cancer, talk to your doctor about a referral to a genetic counsellor or a family cancer clinic to check your risk.

Thyroid conditions

Thyroid nodules, an enlarged thyroid (known as a goitre) or inflammation of the thyroid (thyroiditis), only slightly increase the chance of developing thyroid cancer.

Obesity

Being overweight or obese may increase the risk of developing thyroid cancer.

Iodine levels

Studies have linked having both too much and too little iodine with a possible higher risk of thyroid cancer.

Who gets thyroid cancer?

Around 4000 people are diagnosed with thyroid cancer each year in Australia.

Women are almost 3 times more likely to develop thyroid cancer than men. It’s the 7th most common cancer in Australian women and the most diagnosed cancer in women who are aged 20–24.

Even though people of any age can get thyroid cancer (including children), it is most often diagnosed in women in their 40s and 50s, and men in their 60s and 70s.

Rates of thyroid cancer in Australia have been increasing since the 1980s. What’s causing the rise in cases is unclear. Ultrasound, CT and MRI scans now find smaller thyroid cancers that once weren’t noticed, which may explain some of the increase in cases.

→ READ MORE: Thyroid cancer symptoms