Understanding thyroid cancer

What thyroid cancer is, the main types in plain words (papillary, follicular, medullary and anaplastic), how it is staged, and the tests you may have.

5 min read · last reviewed September 30, 2026

Being told you have thyroid cancer can bring up a lot of feelings at once. You might feel scared, confused or even numb. Many people also hear that thyroid cancer is "very treatable," and still feel worried. Both things can be true.

Learning a few key words can help you follow what your team is saying and ask the questions that matter to you. Here is a plain-language guide.

Your thyroid and what it does

Your thyroid is a small, butterfly-shaped gland at the front of your neck, just below your Adam's apple. It has two halves, called lobes, joined by a thin bridge.

The thyroid makes hormones that help control how your body uses energy. They affect your heart rate, body temperature, weight and energy level.

The thyroid has two main kinds of cells:

• Follicular cells make thyroid hormone. To do this, they take up iodine from your food. Most thyroid cancers start in these cells.
• C cells make a hormone called calcitonin, which plays a small role in handling calcium. Medullary thyroid cancer starts in these cells.

Thyroid cancer happens when cells in the gland start to grow out of control and form a lump, called a tumour. Nothing you did caused it.

The main types of thyroid cancer

Knowing your type is one of the most important facts about your cancer. It guides your whole treatment plan.

Papillary thyroid cancer. This is by far the most common type. It starts in follicular cells and usually grows slowly. It may spread to lymph nodes in the neck, but even then it often responds very well to treatment.

Follicular thyroid cancer. This also starts in follicular cells and usually grows slowly. It is less likely than papillary cancer to spread to lymph nodes. A related type is called oncocytic cancer. You may also hear its older name, Hürthle cell cancer.

Doctors often group papillary and follicular cancer together as differentiated thyroid cancer. That means the cancer cells still look and act a lot like normal thyroid cells. Because they still take up iodine, radioactive iodine treatment can be used for some people.

Medullary thyroid cancer. This starts in the C cells. It is less common. It can make high levels of calcitonin and another marker called CEA, which show up in blood tests. About 1 in 4 medullary cancers runs in families, caused by a change in a gene called RET. That is why everyone with medullary thyroid cancer is offered genetic testing. If you carry the gene change, your close family members can be tested too. Radioactive iodine does not work for this type.

Anaplastic thyroid cancer. This is rare. It grows and spreads quickly, so it needs urgent care from an expert team. Newer treatments, including targeted drugs, have opened up more options. If you have this type, your team will move fast and explain each step with you.

Something you can do: Ask your team, "Which type of thyroid cancer do I have?" and write the answer down.

How thyroid cancer is staged

Staging describes how big the cancer is and whether it has spread. Your team uses it to plan treatment. Stages run from I (1) to IV (4). A lower number means the cancer is more contained.

Staging looks at:

• The tumour: how big it is, and whether it has grown outside the thyroid.
• Lymph nodes: whether cancer has spread to nearby lymph nodes in the neck.
• Spread: whether it has spread to distant parts of the body, such as the lungs or bones.

Thyroid cancer staging is a bit unusual, because age matters for papillary and follicular cancer. For people under 55, there are only two stages. Stage I means the cancer has not spread to distant parts of the body, even if it is in neck lymph nodes. Stage II means it has spread to distant parts. For people 55 and older, the stages use more detail about size and spread.

Medullary cancer is staged by size and spread, not age. All anaplastic cancers are called stage IV, even when found early, because they can spread quickly.

Your team may also talk about your risk of recurrence. This is the chance the cancer could come back. It helps them decide whether you need more treatment, such as radioactive iodine, and how closely to follow you.

Key tests

Neck ultrasound. Sound waves make pictures of your thyroid and neck lymph nodes. It is painless and is often the first test. It is also used for follow-up.

Fine-needle aspiration (FNA) biopsy. A doctor uses a very thin needle, often guided by ultrasound, to take a few cells from the lump. You may feel pressure or a pinch. The results are often reported in one of six groups, from "benign" (not cancer) to "malignant" (cancer). Some results come back "in-between," or indeterminate.

Molecular tests. If a biopsy result is unclear, the cells may be checked for gene changes. This can help show whether a lump is likely to be cancer.

Blood tests. These may include:

• TSH, to check how your thyroid is working.
• Calcitonin and CEA, if medullary cancer is possible.
• Thyroglobulin, a protein made by thyroid cells. It is most useful after treatment. When your thyroid has been removed, a rising level can be an early sign the cancer is back.

Other scans. A CT or MRI scan can show if the cancer has grown into nearby parts of the neck. A PET scan or a radioactive iodine scan may look for spread in some people.

Voice box check (laryngoscopy). The nerves that move your vocal cords run right beside the thyroid. Before surgery, your team may look at your vocal cords with a small camera to see how they move.

Something you can do: Ask for copies of your biopsy and scan reports, and keep them in one folder.

Questions to ask your care team

• What type of thyroid cancer do I have?
• What stage is it, and has it spread to my lymph nodes?
• What is my risk of the cancer coming back?
• Do I need any more tests before treatment?
• If I have medullary cancer, should my family be tested?
• Who can I call if I have questions between visits?

This article is general information, not medical advice. Talk with your health care team about your own situation. In an emergency, call 9-1-1 or your local emergency number.

In an emergency, call 9-1-1 or your local emergency number.

General information, not medical advice. It does not replace your own care team. If you think you or someone else is having a medical emergency, call 9-1-1 or your local emergency number. If you are in crisis or thinking about suicide, call or text 9-8-8 (Canada and the US).

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