Diagnosing thyroid cancer

A thyroid function test and a procedure known as fine-needle aspiration cytology are used to help diagnose thyroid cancer.

If you have any possible symptoms of thyroid cancer, your GP will examine your neck and ask about any associated symptoms you may be experiencing, such as unexplained hoarseness.

The next step is to check whether the swelling in your neck is caused by other problems with your thyroid gland. This is done by carrying out a blood test known as a thyroid function test.

Thyroid function test

The most common cause of swelling in the neck is either an overactive thyroid gland (hyperthyroidism) or an underactive thyroid gland (hypothyroidism). A thyroid function test will help confirm or rule out these conditions.

A thyroid function test measures the amount of certain types of hormones in your blood. Excess levels of the two hormones produced by the thyroid gland, thyroxine and triiodothyronine, indicate an underlying condition that is making your thyroid gland overactive.

If your thyroid gland is underactive, another gland, known as the pituitary gland, will produce a hormone called thyroid stimulating hormone (TSH). TSH is released by your body to stimulate your thyroid gland. Therefore, if you have a high level of TSH in your blood it means your thyroid gland is underactive.

Further tests will be needed if the thyroid function test reveals your thyroid gland is working normally.

Fine-needle aspiration cytology

Fine-needle aspiration cytology (FNAC) is the next stage in diagnosing thyroid cancer. FNAC is an outpatient procedure, which means you will not have to spend the night in hospital.

A small needle will be inserted into the lump in your neck to allow a small sample of cells to be removed. The sample will be studied under a microscope. FNAC can usually reveal whether or not any cancerous cells are present in your thyroid gland and, if they are, what type of thyroid cancer you have.

Further testing

Further testing may be recommended if the FNAC results are inconclusive or if further information is needed to make your treatment more effective. These tests may include:

In most cases, when it has not been possible to rule out thyroid cancer by FNAC, surgery will be recommended to remove the part of the thyroid gland that contains the lump or swelling.


Staging is a way of assessing how far the cancer has spread through the body – the higher the grade, the further it has spread.

It is usually impossible to stage the tumour before the initial treatment has been completed – that is, after surgery and radioactive iodine treatment (see below).

Thyroid cancer can be categorised using a system known as TNM classification, where:

  • T – indicates the size of the tumour
  • N – indicates whether the cancer has spread to nearby lymph nodes (small glands that remove unwanted bacteria from the body)
  • M – indicates whether the cancer has spread to other parts of the body (metastasis)

While widely used, the TNM classification system can sometimes be difficult for someone with little or no medical knowledge to understand. Therefore, the rest of this topic will use a staging system derived from TNM, where the stages of thyroid cancer are described numerically.

Staging for differentiated thyroid cancers (papillary carcinomas and follicular carcinomas) varies with a person’s age because in older people these types of cancers tend to be more aggressive.

Only two stages are used for differentiated thyroid cancers in people under 45 years of age. They are:

  • stage 1 – the cancer may have spread to other lymph nodes in the neck or head, but not to other parts of the body
  • stage 2 – where the cancer has spread to other parts of the body

Four stages are used in cases of differentiated thyroid cancers that occur in people over 45 years of age, and for all cases of medullary thyroid carcinoma. They are:

  • stage 1 – the tumour is no larger than 2cm (0.79 inches) across and has not spread beyond the thyroid gland
  • stage 2 – the tumour is now 2-4cm (0.79-1.57 inches) across but is still contained within the thyroid gland
  • stage 3 – the tumour has spread out of the thyroid gland into nearby lymph nodes
  • stage 4A – the tumour has spread out of the lymph nodes and into other tissues in the neck, such as the muscles, or has spread to the lymph nodes in the upper chest, but not to other parts of the body
  • stage 4B – the tumour has spread to the tissue near the spine but not to other parts of the body
  • stage 4C – the tumour has spread to other parts of the body; usually the bones, the lungs or both

Staging is not usually used for cases of anaplastic thyroid carcinoma because by the time it is diagnosed, the cancer will have spread to another part of the body.

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