Tests for Thyroid Cancer

Sometimes, thyroid cancer is found when a person goes to a doctor because they are having signs or symptoms. It might also be found during a routine physical exam, or during tests done for another reason.

If there is reason to suspect you might have thyroid cancer, your health care team will use one or more tests to confirm your diagnosis. If cancer is found, other tests might be done to find out more about your cancer.

Medical history and physical exam

If you have signs or symptoms that suggest you might have thyroid cancer, your health care provider will ask about your symptoms. They may also ask about your medical history, possible risk factors (including your family history), and any other health problems or concerns you have.

Your doctor will then examine you. During the exam, the doctor will pay special attention to the size and firmness of your thyroid and any enlarged lymph nodes in your neck.

Imaging tests

Imaging tests use x-rays, sound waves, or other ways to look inside your body. These tests might be done for several reasons, including to:

• Help find (or get a better look at) suspicious areas that might be cancer
• Learn how far cancer may have spread
• Help tell if treatment is working

If you have thyroid cancer, or there is reason to believe you might have it, you will likely get one or more of the following imaging tests.

Ultrasound

Ultrasound uses sound waves and their echoes to create images of parts of your body. You are not exposed to radiation during this test.

Ultrasound can help determine if a thyroid nodule is solid or filled with fluid. (Solid nodules are more likely to be cancer.) It can also be used to check the number and size of thyroid nodules, as well as help determine if any nearby lymph nodes in your neck are enlarged, which might be a sign that thyroid cancer has spread.

For thyroid nodules that are too small to feel, ultrasound can be used to guide a biopsy needle into the nodule to get a sample. (See below for more on biopsies.) Even when a nodule is large enough to feel, doctors often prefer to use ultrasound to help guide the needle.

Radioiodine scan

A radioiodine scan can help determine if a lump in your neck is thyroid tissue (which may or may not be cancer). It can also be used in people who have already been diagnosed with differentiated thyroid cancer (papillary, follicular, or oncocytic/Hürthle cell) to help see if it has spread.

Because medullary thyroid cancer (MTC) cells do not absorb iodine, radioiodine scans are not used for this cancer.

How a radioiodine scan works

For this test, a small amount of radioactive iodine (called I-131) is swallowed (usually as a pill) or injected into a vein. Over time, the iodine is absorbed by the thyroid gland (or thyroid cells anywhere in the body). A special camera is used several hours later to see where the radioactivity is located.

During the scan

You might have a thyroid scan or a whole-body radioiodine scan, depending on your situation.

Thyroid scan: During a thyroid scan, the camera is placed in front of your neck to measure the amount of radiation in your thyroid gland.

Areas that take up more radiation are called hot nodules. Hot nodules are usually not cancer. Abnormal areas of the thyroid that have less radioactivity than the surrounding tissue are called cold nodules. Cold nodules can be benign (non-cancerous) or they can be cancerous.

Because both benign and cancerous nodules can appear cold, this test by itself can’t diagnose thyroid cancer.

Whole-body radioiodine scan: After surgery for thyroid cancer, whole-body radioiodine scans can be useful to look for possible cancer spread throughout the body. These scans become even more sensitive if the entire thyroid gland has been removed by surgery, because more of the radioactive iodine is picked up by any remaining thyroid cancer cells.

Increasing TSH levels before the scan

Radioiodine scans work best in people who have high blood levels of thyroid-stimulating hormone (TSH, or thyrotropin).

For people whose thyroid has been removed, TSH levels can be increased by stopping thyroid hormone pills for a few weeks before the test. This leads to low thyroid hormone levels (hypothyroidism) and causes the pituitary gland to release more TSH, which in turn stimulates any thyroid cancer cells to take up the radioactive iodine.

A downside of this is that it can cause the symptoms of hypothyroidism, including tiredness, depression, weight gain, sleepiness, constipation, muscle aches, and reduced concentration. One way to raise TSH levels without withholding thyroid hormone is to give an injectable form of thyrotropin (Thyrogen) before the scan.

Because any iodine already in the body can affect this test, people are usually told to avoid foods or medicines that contain iodine for a few days before the scan.

Using radioactive iodine to treat differentiated thyroid cancer

Radioactive iodine can also be used to treat differentiated thyroid cancer, but it is given in much higher doses. This type of treatment is described in Radioactive Iodine (Radioiodine) Therapy.

Computed tomography (CT) scan

A CT scan uses x-rays to make detailed cross-sectional images of your body. It can help determine the location and size of thyroid cancers and whether they have spread to nearby areas, although an ultrasound of the neck is usually done first. A CT scan can also be used to look for spread into distant organs such as the lungs.

One problem with using CT scans is that the CT contrast dye contains iodine, which can interfere with radioiodine scans. For this reason, many providers prefer to use MRI for differentiated thyroid cancer.

Magnetic resonance imaging (MRI)

MRIs use radio waves and strong magnets instead of radiation to create detailed cross-sectional images of your body. MRI can provide very detailed images of soft tissues such as the thyroid gland and nearby lymph nodes. However, an ultrasound of the neck is usually the first test done to look at the thyroid.

MRI might also be used to look for cancer spread to other parts of the body, although this is less common.

Positron emission tomography (PET) scan

A PET scan can be useful if your thyroid cancer doesn’t take up radioactive iodine. In this situation, the PET scan may be able to tell whether the cancer has spread.

Vocal cord exam (laryngoscopy)

Thyroid cancers can sometimes affect the vocal cords. If you have voice changes, or if you’re going to have surgery to treat thyroid cancer, a procedure called a laryngoscopy may be done to see if your vocal cords are moving normally.

For this exam, the doctor looks down your throat at your larynx (voice box) using either special mirrors or a laryngoscope, a thin tube with a light and a lens on the end for viewing.

Biopsy

The actual diagnosis of thyroid cancer is made with a biopsy. During a biopsy, small pieces from the suspicious area are removed. These pieces are looked at in the lab to see if cancer cells are present.

Doctors usually decide whether a biopsy is needed based on how a thyroid nodule looks during an ultrasound. Some features make it more likely that the nodule is cancer.

Fine needle aspiration (FNA) biopsy

If your doctor thinks a biopsy is needed, the simplest way to find out if a thyroid nodule is cancer is with a fine needle aspiration (FNA). This type of biopsy can sometimes be done in your doctor’s office or clinic.

Before the biopsy, local anesthesia (numbing medicine) might be injected into the skin over the nodule, but in most cases it isn’t needed. The doctor will put a thin, hollow needle directly into the nodule to aspirate (remove) some cells and a few drops of fluid into a syringe. The doctor usually repeats this a few times, taking samples from several areas of the nodule. The biopsy samples are then sent to a lab, where they are looked at to see if they contain cancer cells.

Doctors often use ultrasound to see the thyroid during the biopsy. This helps make sure they are getting samples from the right areas. It is especially helpful for smaller nodules.

FNA biopsies can also be used to get samples of swollen lymph nodes in the neck to see if they contain cancer. Sometimes an FNA will need to be repeated if the samples didn’t contain enough cells.

Other biopsies

Sometimes the test results might come back as “suspicious” or “of undetermined significance” when the FNA findings don’t show for sure if the nodule is cancer or not. If this happens, the doctor may order lab tests on the sample (see below).

If the diagnosis isn’t clear after an FNA, you might need a different type of biopsy to get a larger sample, especially if the doctor has reason to think the nodule may be cancer. This might be done with a core biopsy using a larger needle, a surgical “open” biopsy to remove the nodule, or a lobectomy (removal of half of the thyroid gland).

Surgical biopsies and lobectomies are done in an operating room while you are under general anesthesia (in a deep sleep).

A lobectomy can also be the main treatment for some early cancers, although for many cancers the rest of the thyroid will need to be removed as well (during an operation called a completion thyroidectomy).

Lab tests of biopsy (or other) samples

Your doctor might order molecular tests to look for specific gene changes in the cancer cells. This might be done for a few different reasons:

• For diagnosis: If FNA biopsy results aren’t clear, the doctor might order lab tests on the samples to see if there are changes in the BRAF or RET/PTC genes. Finding one of these changes makes thyroid cancer much more likely.
• For making treatment decisions: For some types of thyroid cancer, molecular tests (sometimes called biomarker tests) might be done to see if the cancer cells have changes in certain genes (such as the BRAF, RET/PTC, or NTRK genes). This could mean that certain targeted drugs might be helpful in treating the cancer, especially if it is advanced.

These tests can be done on samples taken during a biopsy or during surgery for thyroid cancer. If the biopsy sample is too small to do the needed molecular tests, some molecular tests may also be done on blood that is taken from a vein, just like a regular blood draw. This is known as a liquid biopsy. The results of this testing can then be compared with what is already known about the cancer.

Blood tests

Different types of blood tests may be done to see if your thyroid is working normally. The results of these blood tests can help your doctor decide what other tests might be needed.

Blood tests can also be used to monitor certain thyroid cancers.

Thyroid-stimulating hormone (TSH)

To check the overall activity of your thyroid gland, your doctor might test the levels of thyroid-stimulating hormone (TSH or thyrotropin) in your blood. TSH is made by the pituitary gland. Your TSH level might be high if your thyroid isn’t making enough hormones.

This information can be helpful when choosing which imaging tests (such as ultrasound or radioiodine scans) to use to look at a thyroid nodule.

The TSH level is usually normal in people with thyroid cancer.

T3 and T4 (thyroid hormones)

T3 and T4 are the main hormones made by the thyroid gland. Levels of these hormones may be measured to get a sense of thyroid gland function.

The T3 and T4 levels are usually normal in people with thyroid cancer.

Thyroglobulin

Thyroglobulin is a protein made by your thyroid gland. Measuring the thyroglobulin level in the blood can’t be used to diagnose thyroid cancer, but it can often be helpful after treatment.

A common way to treat thyroid cancer is to remove most of the thyroid with surgery and then use radioactive iodine to destroy any remaining thyroid cells. These treatments should lead to a very low level of thyroglobulin in the blood within several weeks.

If this doesn’t happen, it might mean that there are still thyroid cancer cells in the body. If the level rises again after being low, it could be a sign that the cancer has come back.

Calcitonin

Calcitonin is a hormone that helps control how your body uses calcium. It is made by C cells in the thyroid. C cells are the cells that can develop into medullary thyroid cancer (MTC).

If MTC is suspected, or if you have a family history of the disease, blood tests of calcitonin levels can help look for MTC. This test is also used to look for the possible recurrence of MTC after treatment. Calcitonin can affect blood calcium levels, so this might be checked as well.

Carcinoembryonic antigen (CEA)

People with MTC often have high blood levels of a protein called carcinoembryonic antigen (CEA). Tests for CEA can help monitor this type of thyroid cancer.

Other blood tests

You might have other blood tests as well. For example, if you are scheduled to have surgery, tests will be done to check your blood cell counts, to look for bleeding disorders, and to check your liver and kidney function.

If you have medullary thyroid carcinoma (MTC) and are scheduled to have surgery, you might need additional blood tests to check for tumors called pheochromocytomas. MTC is sometimes caused by a genetic syndrome that can also result in this type of tumor. Pheochromocytomas can release hormones that might cause problems during surgery while you are under anesthesia (in a deep sleep).

Tests to check for pheochromocytomas can include blood tests for epinephrine (adrenaline) and a related hormone called norepinephrine, and/or urine tests for their breakdown products (called metanephrines).