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Diagnosing thyroid cancer

This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on June 7, 2022.

The first step in developing a personalized thyroid cancer treatment plan is getting an accurate diagnosis. Various laboratory tests and procedures designed for diagnosing thyroid cancer are used to evaluate and stage the disease. For example, an ultrasound may help the oncologist inspect the thyroid for nodules, and a biopsy may be taken to retrieve and test tissue samples to learn whether a thyroid nodule is cancerous. An X-ray of the chest may reveal whether cancer has spread to the lungs.

Common tests used for diagnosing thyroid cancer include:

Biopsy

A sample of throat tissue or cells is required for a biopsy, which must be conducted before treatment can begin. A biopsy, in which cells from the suspicious area of the thyroid gland are removed and sent to a lab, is the only way to accurately diagnose thyroid cancer. A pathologist examines the tissue sample with a microscope to look for cancer cells. If they’re found, this means thyroid cancer is present.

The types of biopsies typically used for diagnosing head and neck cancers are:

Fine-needle aspiration (FNA): With this test, a very thin needle attached to a syringe is used to extract (aspirate) cells from a nodule or lump on the thyroid gland. An FNA is typically done in your doctor’s office or clinic and under local anesthesia so you shouldn’t feel pain or discomfort. Patients usually can drive themselves home after the procedure.

An FNA is a safe and well-tolerated procedure, but there’s always a small risk of side effects. After your biopsy, you may notice the following:

  • Skin bruising or soreness in the area where the biopsy was taken
  • Bleeding
  • Infection
  • Formation of cysts

Always call your care team if you don’t feel well after the procedure.

Surgical biopsy: If the results of the FNA biopsy are inconclusive, your doctor may recommend a surgical biopsy. This procedure is typically done under general anesthesia, and it may require an overnight stay in the hospital. During the surgery, your doctor removes the suspicious nodule and possibly the lobe of the thyroid gland where it grew. A pathologist later checks these tissues for cancer cells.

If you’re scheduled to undergo a surgical biopsy, your care team can talk you through the process and let you know what to expect.

Imaging tests

X-ray: An X-ray of the chest may be taken to check if the cancer has spread to the lungs. Cancer will not be present in the lungs unless it is in an advanced stage.

CT scan: Computed tomography (CT) scan (also known as a computed axial tomography scan, or CAT scan) is one of the most commonly used tools for the screening, diagnosis and treatment of cancer. This test for thyroid cancer is usually used to see if the disease has spread to other areas of the body, but it may also sometimes be used to guide the biopsy needle. However, CT scans with contrast use a dye that contains iodine, a substance known to interfere with the scanning process. Many doctors are now using magnetic resonance imaging (MRI) scans more than CT scans to avoid this issue.

MRI: Magnetic resonance imaging is an imaging tool designed to create detailed, cross-sectional pictures of the inside of the body. Using radiofrequency waves, powerful magnets and a computer, MRI systems may distinguish between normal and diseased tissue. MRI may be used to look at the brain and spinal cord, locations where thyroid cancer may spread (metastasize).

Nuclear medicine scan: The most common test used for patients with thyroid cancer is a radioiodine scan, which involves swallowing a small amount of radioactive iodine, or I-123. This test is often used in patients with differentiated forms of the disease (papillary, follicular, Hürthle cell). It may be used to identify abnormal areas of the thyroid gland, or to determine whether the cancer has spread to other areas of the body. During a thyroid scan, your doctor gives you a small amount of radioactive iodine, either orally or via an injection. After a few hours, the substance is absorbed by the thyroid gland. Your doctor uses a special camera placed in front of your neck to measure the radiation levels. Areas of the thyroid that are abnormal will absorb less radioactive iodine than normal tissue and are called cold nodules. Areas that absorb more radiation are called hot nodules. While hot nodules usually don’t indicate cancer, cold nodules can be either benign or malignant. Doctors usually can’t diagnose cancer with only this thyroid scan and use other imaging tests for a more complete assessment. Additionally, this test isn’t used for medullary thyroid cancer (MTC) because medullary thyroid cells are unable to absorb iodine.

PET/CT scan: Positron emission tomography (PET) is a nuclear imaging technique that creates detailed, computerized pictures of organs and tissues inside the body. PET scans are very sensitive, but they do not show much detail, so they will often be performed in combination with a CT scan (called PET/CT).

Ultrasound: Also known as sonography, this non-invasive procedure can help doctors determine the size of nodules on the thyroid and see how many are present. It may also help determine whether the suspected nodule is solid or filled with fluid. This is useful information for you and your care team, as solid nodules have a higher risk of being cancerous. Sometimes, an ultrasound is also used to guide the biopsy needle when nodules are small.

Blood tests

Various laboratory tests are used to diagnose thyroid cancer. They include:

Advanced genomic testing: Genomic testing examines a tumor on a genetic level to look for the DNA alterations that drive the growth of cancer. By identifying the mutations that occur in a cancer cell's genome, your care team can better understand what caused the tumor and tailor treatment based on these findings. Genetic testing may be used when MTC is suspected because this cancer type is linked to a specific genetic condition. If your doctor is concerned about MTC, you may need to undergo advanced genetic testing and a blood test for tumor markers such as the carcinoembryonic antigen (CEA) protein and the calcitonin hormone.

Nutrition panel: With this test, we evaluate patients for deficiency of nutrients, such as vitamin D and iron. The test helps us identify the nutrients patients need replaced or boosted to support their quality of life.

Other lab tests that may be used include a thyroid function test, as well as level tests of the thyroid-stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4). Levels of the protein thyroglobulin are also typically tested before and after surgery.

Laryngoscopy

A laryngoscopy is often used to examine the back of the throat. The two types of laryngoscopy are indirect laryngoscopy and direct laryngoscopy. Because the thyroid gland is so close to the vocal cords, thyroid tumors may sometimes affect them. For this reason, your doctor may want to examine the cords first with special tools, such as a laryngoscope, if you are scheduled for surgery.

Next topic: How is thyroid cancer treated?

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