Thyroid cancer

On this page:

What is thyroid cancer?

Thyroid cancer happens when cells in your thyroid change and start to grow in an abnormal way. A group of these cancer cells can form a tumour. Thyroid cancer can affect how your thyroid works and cause symptoms. 

About 280 people are diagnosed with thyroid cancer in Ireland every year.*

What is the thyroid and what does it do?

Your thyroid is a gland at the base of your neck, just below your Adam's apple. It sits on top of your windpipe and below your voicebox (larynx).

It is shaped like a butterfly because the gland is in 2 halves. The halves are connected by a narrow bridge of thyroid tissue called the isthmus. The 2 halves are called the lobes of the thyroid. The thyroid is part of a network of glands that make up your endocrine system.

Thyroid hormones

Your thyroid makes hormones that keep your heart rate, blood pressure, body temperature and weight at the right levels. 

The thyroid gland releases three separate hormones:

• T3, which is known as triiodothyronine 
• T4, which is known as thyroxine 
• Calcitonin

The T3 and T4 hormones help regulate the body's metabolic rate. The metabolic rate is how fast the various processes of the body work, such as how quickly the body burns calories.

Excess levels of T3 and T4 in the body would make someone to feel overactive and cause them to lose weight. 

Not enough T3 and T4 would make feel someone feel 'slow' and sluggish, and cause them to gain weight.

Calcitonin helps control the levels of calcium in your blood. Calcium is a mineral that has many important functions, such as building strong bones.

Medical content updated from our 'Understanding thyroid cancer' booklet (2022) reviewed by Prof Marie Louise Healy, Consultant Endocrinologist; Cristina Domsa, Clinical Nurse Specialist Endocrinology

*The Irish Cancer Society uses the most up-to-date cancer statistics from the National Cancer Registry Ireland, available on www.ncri.ie