Thyroid Cancer - Diagnosis

Approved by the Cancer.Net Editorial Board, 09/2016

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. To see other pages, use the menu.

Doctors use many tests to find, or diagnose, cancer. They also do tests to learn if cancer has spread to another part of the body from where it started. If this happens, it is called metastasis. For example, imaging tests can show if the cancer has spread. Imaging tests show pictures of the inside of the body. Doctors may also do tests to learn which treatments could work best.

For most types of cancer, a biopsy is the only sure way for the doctor to know whether an area of the body has cancer. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis.

Your doctor may consider these factors when choosing a diagnostic test:

  • The type of cancer suspected

  • Your signs and symptoms

  • Your age and medical condition

  • The results of earlier medical tests

The list below describes options for diagnosing this type of cancer. Not all tests listed below will be used for every person.

  • Physical examination. The doctor will feel the neck, thyroid, throat, and lymph nodes (the tiny, bean-shaped organs that help fight infection) in the neck for unusual growths or swelling. If surgery is recommended, the larynx may be examined at the same time with a laryngoscope, which is a thin, flexible tube with a light.

  • Blood tests. There are several types of blood tests that may be done during diagnosis and to monitor the patient during and after treatment. This includes tests called tumor marker tests. Tumor markers are substances found at higher-than-normal levels in the blood, urine, or body tissues of some people with cancer.

    • Thyroid hormone levels. As explained in the Introduction, thyroid hormones regulate a person’s metabolism. The doctor will use this test to find out the current levels of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the body.

    • Thyroid-stimulating hormone (TSH). This blood test measures the level of TSH, a hormone produced by the pituitary gland near the brain. If the body is in need of thyroid hormone, the pituitary gland releases TSH to stimulate production.

    • Tg and TgAb. Thyroglobulin (Tg) is a protein made naturally by the thyroid as well as by differentiated thyroid cancer. After treatment, there should be very low levels of thyroglobulin in the blood since the goal of treatment is to remove all thyroid cells. If Tg is rising after surgery and/or radioactive iodine, it may be a sign of more cancer. A tumor marker test may be done to measure the body’s Tg level before, during, and/or after treatment. There is also a test for thyroglobulin antibodies (TgAb), which are proteins produced by the body to attack thyroglobulin that occur in some patients. If TgAb is found, it is known to interfere with the results of the Tg level test.

    • Medullary type-specific tests. If MTC is a possibility, the doctor will order tumor marker tests to check for high calcitonin and carcinoembryonic antigen (CEA) levels. The doctor should also recommend a blood test to detect the presence of RET proto-oncogenes (see Risk Factors), particularly if there is a family history of MTC.

  • Ultrasound. An ultrasound uses sound waves to create a picture of the internal organs. An ultrasound wand or probe is guided over the skin of the neck area. High-frequency sound waves create a pattern of echoes that show the doctor the size of the thyroid gland and specific information about any nodules, including whether a nodule is solid or a fluid-filled sac called a cyst.

  • Biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis. The way to determine whether a nodule is cancerous or benign is through a biopsy. During this procedure, the doctor removes cells from the nodule that are then examined by a cytopathologist. A cytopathologist is a doctor who specializes in analyzing cells and tissue to diagnose disease. This test is often done with the help of ultrasound.

    A biopsy for thyroid nodules will be done in 1 of 2 ways:

    • Fine needle aspiration. This procedure is usually performed in a doctor’s office or clinic. It is an important diagnostic step to find out if a thyroid nodule is benign or cancerous. A local anesthetic may be injected into the skin to numb the area before the biopsy. The doctor inserts a thin needle into the nodule and removes cells and some fluid. The procedure may be repeated 2 or 3 times to get samples from different areas of the nodule. The report is created by the cytopathologist. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease. The test can be positive, meaning there are cancerous cells, or negative, meaning there are no cancerous cells. The test can also be undetermined, meaning it is not clear whether cancer is there. Unfortunately, it can be possible to miss the targeted area.
    • Surgical biopsy. If the needle aspiration biopsy is not clear, the doctor may suggest a biopsy in which the nodule and possibly the affected lobe of the thyroid will be removed. This procedure is usually done under general anesthesia. It may also require a hospital stay.

  • Molecular testing of the tumor. Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Results of these tests will help decide whether your treatment options include a type of treatment called targeted therapy (see Treatment Options).

  • Radionuclide scanning. This test may also be called a whole-body scan. This scan will either be done using I-131 or I-123. It is used most often to learn more about a thyroid nodule. In this test, the patient swallows a very small, harmless amount of radioactive iodine, which is absorbed by thyroid cells. This makes the thyroid cells appear on the scan image, allowing the doctor to see differences between those cells and other body structures.

  • X-ray. An x-ray is a way to create a picture of the structures inside of the body, using a small amount of radiation. For instance, a chest x-ray can help doctors determine if the cancer has spread to the lungs.

  • Computed tomography (CT or CAT) scan. A CT scan creates a 3-dimensional picture of the inside of the body using x-rays taken from different angles. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. A CT scan can also be used to measure the tumor’s size. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill to swallow.

    CT scans are often used in patients with thyroid cancer to examine parts of the neck that cannot be seen with ultrasound (see above). Also, CT scans of the chest may be needed to look to see if thyroid cancer has spread. CT scans of the abdomen may be used to see if thyroid cancer has spread to the liver or other sites. Patients with the hereditary form (see Risk Factors) of medullary thyroid cancers may be at risk for developing other types of endocrine tumors in the abdomen; these patients may also have a CT scan of the abdomen.

  • Positron emission tomography (PET) or PET-CT scan. A PET scan is usually combined with a CT scan (see above), called a PET-CT scan. However, you may hear your doctor refer to this procedure just as a PET scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive sugar substance is injected into the patient’s body. This sugar substance is taken up by cells that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.

After diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is thyroid cancer, these results also help the doctor describe the cancer. This is called staging.

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the disease. Or, use the menu to choose another section to continue reading this guide.