What is thyroid cancer?

Thyroid cancer is when abnormal cells in the thyroid gland start to divide and grow in an uncontrolled way. Without treatment, cancer cells can eventually grow into surrounding healthy tissues and may spread to other areas of the body.

 The thyroid gland sits in the throat. This 2 minute video describes the different parts of the throat.

The thyroid gland

The thyroid is a small butterfly shaped gland that makes and releases hormones. It’s found at the front of your neck in the lowest part, just behind the small hollow where your collar bones meet. You can’t usually feel a thyroid gland that is normal.

The thyroid gland is in 2 halves called lobes. They are connected together by a thinner bridge of thyroid tissue. The bridge is called the isthmus.

A thyroid cancer is usually found in just one lobe. But some types of thyroid cancer can be found in both lobes. 

Diagram showing the thyroid gland

What does the thyroid gland do?

The thyroid gland makes hormones which affect the way your body works.

T3 and T4

T3 (tri iodothyronine) and T4 (thyroxine) are the main hormones that your thyroid gland makes. They help to control your metabolic rate which is the speed of your body processes. For example, these hormones help to control your digestion, muscles and heart.

You might put on weight and feel very tired and lacking in energy if your thyroid gland doesn't make enough T3 and T4.

You can lose weight, despite an increased appetite, if your thyroid gland makes too much of these hormones. You might also feel anxious and find it difficult to relax.


Calcitonin is another hormone produced by the thyroid gland. It helps to control the amount of calcium circulating in the blood. Calcitonin works with a hormone called parathyroid hormone to do this.

Parathyroid hormone is made by parathyroid glands. These sit behind and are attached to the thyroid gland.

Too much calcium can make you feel sick and drowsy. Too little can cause nerve problems, such as pins and needles, making muscles twitch and jerk.

The parathyroid glands are left behind if you have your thyroid gland removed. But they can be affected by the operation and may take a while to get back to normal.

Your doctor will check your calcium levels regularly and might give you calcium supplements if needed.

How common is thyroid cancer?

Thyroid cancer is quite rare. Around 3,900 people are diagnosed in the UK each year. It’s more common in women than in men.

There are factors that can increase the risk of developing thyroid cancer, including radiation and some types of non cancerous thyroid conditions.

Last reviewed: 
17 Feb 2021
Next review due: 
19 Feb 2024
  • Thyroid cancer statistics
    Accessed February 2021

  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser
    Wiley Blackwell, 2015

  • Ross and Wilson Anatomy and Physiology in Health and Illness (12th edition)    
    A Waugh and A Grant
    Churchill Livingstone, 2014

Related links