The thyroid gland lies at the base of the neck. Learn more with this 3D animation.

What is thyroid cancer?

Cancer occurs when cells become abnormal, grow uncontrollably and have the potential to spread to other parts of the body. These cells build up to form a mass (or lump). 
There are four main types of thyroid cancer, most of these come from the follicular cells that make thyroid hormone.
Papillary  This is the most common type of thyroid cancer (about 75% of all cases). It tends to grow very slowly, but often spread to lymph nodes. It can be cured or controlled in most people and is rarely fatal.
Follicular  This accounts for about 5-10% cases. It grows slowly and tends to stay in the thyroid, however it can spread to the lungs or bones if diagnosed late. If diagnosed early, most people with follicular thyroid cancer can be treated successfully.
Anaplastic  This type of thyroid cancer is rare (less than 1%) but these are very aggressive
Medullary  This is different to other thyroid cancers because they develop in cells called ‘C cells’ that do not produce thyroid hormone. 

Poorly differentiated thyroid cancer makes up to 5% of thyroid cancer, which usually occurs in older people and can frequently be non iodine-avid

What causes thyroid cancer?

Doctors often can’t explain why a person gets cancer. But we do know what makes some cancers more likely.

The two main causes of thyroid cancer are: 
  • being female: In Australia women are about four times more likely than men to get thyroid cancer

  • age: while thyroid cancer can occur at any age, it is most common in people aged 40–60 years.

Having a diet low in iodine increases risk of thyroid cancer, but this is rare in Australia as iodine is added to salt and other foods.

Other factors that increase the risk of thyroid cancer include: 
Radiation - this is a very important risk factor for thyroid cancer, either because of medical treatment (particularly low dose radiation treatment in childhood), or from environmental exposure such as atomic explosions or nuclear fallout
Having a non-cancerous (benign) thyroid disease - like an enlarged thyroid (goitre), thyroid nodules (adenomas) or inflammation of the thyroid (thyroiditis), or having one of these conditions in your family
A family history of thyroid cancer or an inherited gene change (mutation) in the RET oncogene (a protein coding gene)