How is thyroid cancer diagnosed?

A blood test cannot diagnose thyroid cancer, but you will have a blood test to check your levels of T3, T4 and thyroid-stimulating hormone (TSH). The thyroid generally functions normally even if thyroid cancer is present, and your hormone production won’t be affected. However, this blood test may rule out benign thyroid conditions, such as hypothyroidism or hyperthyroidism.

If your doctor suspects you may have medullary thyroid cancer, the levels of calcitonin in the blood may also be checked. High levels of calcitonin in the blood can be a sign of this type of thyroid cancer.

The best way to get detailed information about your thyroid is with an ultrasound. This scan can show the size of any thyroid nodule and whether it is full of fluid or solid. It can also show whether a nodule has any features that suggest it may be a thyroid cancer rather than a benign nodule, and whether the lymph nodes in the neck appear to be affected.

An ultrasound is painless and takes about 15–20 minutes. A gel is spread over your neck, then a handheld device called a transducer is moved over the area. This creates a picture of the internal structure of your thyroid on a computer monitor. An ultrasound uses soundwaves and does not expose you to any radiation.

If you have a thyroid nodule or enlarged lymph node in your neck, you may need a fine needle aspiration (FNA) biopsy. This is an outpatient procedure that takes about 15–30 minutes. If you are having an FNA biopsy:

• the area may be numbed with a local anaesthetic – the procedure can sometimes be uncomfortable, although it is usually not painful
• a thin needle is inserted into the nodule to collect a sample of cells
• ultrasound may be used to guide the needle to the right spot.

The sample is sent to a laboratory, and a specialist doctor called a pathologist examines the sample under a microscope to see whether it contains cancer cells.

You should get the results of the biopsy within a week. If it’s still unclear whether the nodule or enlarged lymph node is cancerous, you may need surgery to remove half of the thyroid (partial thyroidectomy). This will help confirm the diagnosis.

Genetic tests – You may be given the option of sending the biopsy sample overseas to test for changes (mutations) in the genes. Some thyroid cancers with mutations in the BRAF or RAS genes tend to respond to particular treatments. These genetic mutations are due to changes in the cancer cells – they are not the same thing as genes passed through families. Genetic tests for thyroid cancer are not yet routine in Australia and can be expensive.

To see if the cancer has spread from the thyroid to other parts of your body, you may have a CT (computerised tomography) scan and/or a PET (positron emission tomography) scan. This process is called staging. Some scans may be repeated after treatment to see how well the treatment has worked.

CT scan

A CT scan uses x-rays and a computer to create a detailed picture of an area inside the body.

In most cases, an ultrasound provides the information your doctor needs to make a diagnosis. However, you may need a CT scan if your thyroid is very enlarged, if it extends below the collarbone, or if your doctor suspects that the cancer has spread to other areas in the neck. Before the scan, a special dye known as contrast may be injected into one of your veins. This helps ensure that anything unusual can be seen more clearly on the pictures. The dye may make you feel flushed or hot, and it may produce a strange taste in your mouth for a few minutes.

The CT scanner is a large, doughnut-shaped machine. You will lie on a table that moves in and out of the scanner. You will be asked to remain still and hold your breath for a few seconds during the scan. While it may take 30–60 minutes to prepare for the scan, the scan itself takes only a few minutes. You can go home once the scan is finished.

PET scan

A PET scan is rarely needed for thyroid cancer. However, it may be useful in some types of thyroid cancer, particularly if other tests give conflicting results.

To prepare for the PET scan, you will usually be asked not to eat or drink for a period of time (fast). Before the scan, you will be injected with a glucose solution containing a small amount of radioactive material. Cancer cells show up brighter on the scan because they take up more of the glucose solution than normal cells do.

You will be asked to sit quietly for 30–90 minutes while the glucose solution moves around your body. You will then have a scan of your entire body to locate any cancer cells. The scan itself takes about 30 minutes.

Before having scans, tell the doctor if you have any allergies or have had a reaction to contrast during previous scans. You should also let them know if you have diabetes or kidney disease or are pregnant.