Thyroid cancer

Saturday 1 February, 2014

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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 it? | Key points

The thyroid gland

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 communicate with the body and bring about changes. The thyroid gland makes hormones that help 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.

What the thyroid gland does

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.
A hormone involved in controlling calcium levels in the body.

The thyroid gland needs iodine – found in foods such as seafood, iodised table salt, some mineral supplements and dairy products – 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.

The thyroid gland

Behind the thyroid glands are the parathyroid glands. These four glands produce hormones that control the amount of calcium and phosphorus in the blood.

Thyroid hormones

The thyroid gland is controlled by the pituitary gland, which is found in the brain. The pituitary gland is regulated by another gland found in the brain called the hypothalamus.

When your body needs more hormones (T4 and T3), the pituitary gland produces thyroid-stimulating hormone (TSH), which prompts the thyroid gland to produce and release more T4 and T3.

The change in thyroid hormone levels can cause changes to how your cells respond (metabolism):

  • Underactive thyroid (hypothyroidism) – The thyroid gland produces too few hormones causing the metabolism to slow down. You may feel tired and lethargic and gain weight easily.
  • Overactive thyroid (hyperthyroidism) – The thyroid gland produces too many hormones causing the metabolism to speed up. You may lose weight, have an increased appetite, feel shaky and anxious, or have rapid, strong heartbeats (palpitations).

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

Types of thyroid cancer
papillary hyroid cancer
  • most common type (about 70–80% of all cases)
  • develops from the follicular cells
  • tends to grow slowly
follicular thyroid cancer
  • about 25% of thyroid cancer cases
  • develops from the follicular cells
  • includes Hürthle cell carcinoma, a rare subtype
medullary thyroid cancer
  • about 4% of all thyroid cancers
  • develops from the parafollicular cells (C-cells)
  • can run in families
anaplastic thyroid cancer
  • a rare thyroid cancer (1% of cases)
  • may develop from undiagnosed papillary or follicular thyroid cancer
  • usually grows quickly and affects elderly people
thyroid sarcoma or lymphoma
  • these rare types of cancer are not covered in this booklet – talk to your medical team or call Cancer Council Helpline 13 11 20 for information

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
  • difficulty swallowing or breathing
  • a hoarse voice
  • swollen lymph glands in the neck, which may slowly grow in size over months or years
  • gastrointestinal changes, such as diarrhoea and constipation.

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.

A cancerous thyroid usually continues to produce hormones. However, an underactive or overactive thyroid (hypothyroidism or hyperthyroidism) is not typically a symptom of 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.

Exposure to radiation

A small number of thyroid cancer cases are due to having radiotherapy treatment 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.

The most common source of radiation for the average person is an x-ray scan, however the risk of developing thyroid cancer after an x-ray is minimal.

Family history

Some people inherit a faulty gene called the RET gene, which increases their risk of developing thyroid cancer. This may occur in familial medullary thyroid cancer (FMTC) or multiple endocrine neoplasia (MEN).

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, may increase your chance of developing thyroid cancer.

The thyroid needs iodine to make hormones. Iodine is found in iodised salt, dairy products, seafood and eggs. Since 2009, iodine has been added to bread in Australia to help reduce the rate of iodine deficiency.

How common is it?

About 2400 people are diagnosed with thyroid cancer each year in Australia. Thyroid cancer is much more common in females – it is the seventh most common cancer affecting Australian women.

The average age of a woman diagnosed with thyroid cancer is 49; the average age of a man diagnosed with thyroid cancer is 54.

Thyroid cancer cases have increased over the years. Between 1991 and 2009, cases of thyroid cancer increased by 250%. Research is being done to determine the cause of this increase. The number may have increased because there are better ways to earlier detect small cancers that previously went undiagnosed.

Key points

  • 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 patients 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 many cases, thyroid nodules are a symptom of a goitre. This is when the thyroid becomes enlarged, and it is a benign condition (not cancer).
  • An underactive or overactive thyroid (hypothyroidism or hyperthyroidism) isn’t usually a sign that you have thyroid cancer.
  • The cause of thyroid cancer is usually unknown, but it may be caused by exposure to radiation, family history or a benign thyroid disease.
  • About 2400 people are diagnosed with thyroid cancer each year. It’s more common in women.

† Australian Institute of Health and Welfare & Australasian Association of Cancer Registries 2012. Cancer in Australia: an overview, 2012. Cancer series no. 74. Cat. no. CAN 70. Canberra: AIHW.

Reviewed by: Dr Kiernan Hughes, Endocrinologist, San Clinic Specialist Rooms & Chatswood Rooms, Northern Endocrine Pty Ltd, NSW; Dr Daniel Badger, Medical Physicist, The Queen Elizabeth Hospital, SA; Dr Gabrielle Cehic, Nuclear Medicine Physician, Flinders Medical Centre, Lyell McEwin Hospital and The Queen Elizabeth Hospital, SA; Dr Ganessan Kichenadasse, Staff Specialist, Medical Oncologist, Flinders University School of Medicine, SA; Dr Christine Lai, Breast and Endocrine Surgeon, The Queen Elizabeth Hospital, SA; Jenny Lane, Consumer; Janny Wagenaar, Cancer Support Coordinator, Cancer Council TAS; and Cancer Council QLD Helpline Operators.
Updated: 01 Feb, 2014