Your type of thyroid cancer depends on the type of cell the cancer starts in. There are different types of thyroid cancer including:
- papillary thyroid cancer
- follicular thyroid cancer
- oncocytic cell (hurthle cell) thyroid cancer
- medullary thyroid cancer
- anaplastic thyroid cancer
Papillary thyroid cancer is the most common type.
How do doctors diagnose your type of thyroid cancer?
Doctors use a system for classifying thyroid tumours into types. This system is regularly updated. The latest is the World Health Organisation (WHO) classification of 2022.
Based on the latest WHO classification, we give a simple description of some of the types. You can also speak to your doctor or nurse specialist if you want more information about your diagnosis.
To diagnose thyroid cancer, a specialist doctor (pathologist) examines a sample of thyroid cells under the microscope. They look at several factors to group (classify) the different types of thyroid cancers. These factors include:
The type of cell they develop from
There are 2 main types of cell in the thyroid gland. These are:
- follicular cells
- C cells, that make calcitonin
Most thyroid cancers start in follicular cells. This includes:
- papillary thyroid cancer
- follicular thyroid cancer
- oncocytic (hurthle cell) thyroid cancer
A small number of thyroid cancers start in the C cells. These are called medullary thyroid cancers.
How abnormal the cells look (differentiation and grade)
Differentiation means how different the thyroid cancer cells look under a microscope, compared to normal thyroid cells.
Thyroid cancer can be:
- differentiated - the cancer cells look a lot like normal thyroid cells
- poorly differentiated - the cancer cells look less like normal thyroid cells
- undifferentiated - the cancer cells do not look or behave like normal thyroid cells
The grade of a cancer tells you how the cancer might behave. The grade depends on what the cells look like, as well as other factors including:
- how many cells are dividing (the mitotic count) – this shows how quickly the cancer might grow
- how much dying tissue there is (necrosis)
The genetic changes found in the tumour
Your doctor looks to see if there are certain gene changes in the cancer cells. These tests are also called biomarker or molecular studies. The results of these tests help the doctors work out your type of thyroid cancer.
Differentiated thyroid cancer
About 90 out of 100 thyroid cancers (about 90%) are differentiated cancers that start in follicular cells. Differentiated thyroid cancers tend to grow slowly. These include papillary, follicular and oncocytic thyroid cancer.
Papillary thyroid cancer
This is the most common type of thyroid cancer. It is more common in women and is most common in people in their 30s and 40s.
It is usually slow growing, but it can sometimes spread to lymph nodes in the neck or close to the thyroid.
Follicular thyroid cancer
Follicular thyroid cancer is most common in people aged between 40 and 60 and it is more common in women.
Follicular thyroid cancer sometimes spreads to other parts of the body, such as the lungs or bones.
Oncocytic (Hurthle cell) thyroid cancer
Oncocytic thyroid cancer is a rare type of thyroid cancer, also called Hurthle cell thyroid cancer. It used to be grouped with follicular thyroid cancers as it shares some similarities.
Oncocytic cells look different to follicular cells. The cells are also called oxyphilic cells, so this cancer is sometimes called oxyphil cell cancer. Oncocytic tumours can be non cancerous (benign) or cancerous. Benign tumours are called oncocytic adenomas. Oncocytic thyroid cancer can sometimes spread to lymph nodes or to other parts of the body.
Oncocytic thyroid cancer is most often diagnosed in people older than 40, and is more common in women.
High grade thyroid cancers that start in follicular cells
The pathologist looks at the thyroid cancer under the microscope to find out the grade. They look at a number of features. Some follicular, papillary or oncocytic thyroid cancers are high grade. This means they have features such as:
- a high number of cells dividing (a high mitotic count)
- the cancer contains dying tissue (necrosis)
Doctors call these thyroid cancers follicular derived thyroid cancer, high grade. Depending on how abnormal the cells look, these high grade cancers are:
- differentiated high grade thyroid cancer
- poorly differentiated thyroid cancer
These rare cancers tend to grow more quickly than other types of thyroid cancer.
Differentiated high grade thyroid cancer
Differentiated high grade thyroid cancer cells still look similar to normal thyroid cells. But they have other high grade features.
They are often diagnosed at a later stage than other types of thyroid cancer. Some treatments might not work as well and you might need more intense treatment. The doctors might follow you more closely when you finish treatment in case the cancer comes back.
Poorly differentiated thyroid cancer
The cells in poorly thyroid cancer look less like normal thyroid cells than differentiated thyroid cancer cells. These rare cancers tend to grow more quickly than other types of thyroid cancer.
Medullary thyroid cancer
This is a rare type of thyroid cancer. It starts in the C cells in the thyroid.
About a quarter (about 25%) of medullary thyroid cancers are caused by an inherited faulty gene which runs in the family.
Medullary thyroid cancer can spread to other parts of the body, such as the liver or lungs.
Anaplastic thyroid cancer
This is the least common and most serious thyroid cancer.
Anaplastic thyroid cancer is usually diagnosed in older people and is more common in women.
It is called undifferentiated because the cancer cells do not look very like normal thyroid cells. It tends to grow more quickly than other types of thyroid cancer.
It is possible for a lymphoma to develop in the thyroid gland. A primary thyroid lymphoma is a type of non-Hodgkin lymphoma and treatment is similar to that of a lymphoma.
Another rare type of thyroid cancer is sarcoma of the thyroid gland. This might be treated with surgery, chemotherapy or radiation.