How Thyroid Cancer Is Diagnosed

thyroid cancer diagnosis
Illustration by Verywell 

Comprehensive and thorough diagnosis of thyroid cancer involves a number of procedures and tests. Usually, the process of evaluating for thyroid cancer starts with finding a lump or nodule in your gland. You may find it or see it yourself or, in some cases, your doctor may detect it during an exam. It's also fairly common for thyroid nodules to be discovered when you have X-rays of your head or neck for other purposes.

Self-Checks

Examining your neck can sometimes help you find lumps or enlargements that may point to thyroid conditions, including nodules, goiter, and thyroid cancer. You can do a test at home to help detect nodules, which—if noticed—should be brought to your doctor's attention for further evaluation.

To underscore the importance of early detection, the American Association of Clinical Endocrinologists (AACE) encourages Americans to perform a simple self-exam they call the Thyroid Neck Check. While it is not conclusive and may not enable you to detect all nodules (most can't be seen or felt), those that are closer to the surface or large may be found with this simple test.

To detect a thyroid abnormality early or lumps that may indicate potential thyroid cancer, follow these steps:

  1. Stand in front of a mirror.
  2. Take a sip of water and hold it in your mouth.
  3. Stretch your neck back and swallow the water.
  4. Look for an enlargement in your neck below your Adam's apple, above your collarbone.
  5. Feel the area to confirm an enlargement or bump.
  6. If any bump or enlargement is detected, see your doctor as soon as possible.

Again, this self-check does not replace an exam by a medical professional. A thorough examination by a physician is needed to diagnose or rule out thyroid cancer.

Physical Exam

Your doctor will likely first conduct a thorough physical exam. This exam should include palpation of your thyroid, where your doctor physically feels for enlargement and lumps in your thyroid gland and assesses the gland's size, asymmetry, and the firmness. Your doctor will also look for any enlarged lymph nodes in your neck and the area around the gland.

Keep in mind that thyroid nodules are very common. Most, however, are benign (non-cancerous). According to the American Cancer Society, about two or three in 20 thyroid nodules are cancerous.

Tests and Procedures

There are a variety of tests and procedures that your doctor may use to diagnose thyroid cancer and rule out other thyroid conditions.

Blood Tests

Blood tests cannot diagnose thyroid cancer itself or detect a cancerous thyroid nodule, but they can rule out other conditions and determine if your thyroid is working the way it should. Blood tests your doctor may use include:

  • Thyroid-stimulating hormone (TSH): Your doctor may check the TSH level in your blood to evaluate your thyroid's activity and test for hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). This test's results can help your doctor determine which imaging tests to do to visualize your nodule, depending on the result. That said, with thyroid cancer, your TSH level is typically normal.
  • T3 and T4: These are the main hormones that your thyroid makes. Your doctor may test your levels to check how your thyroid is functioning. Like TSH, these hormone levels are usually normal when you have thyroid cancer. 
  • Calcium: When medullary thyroid cancer is suspected, your doctor will typically test for high levels of calcium, as this can be an indicator of the disease.
  • Thyroglobulin: The thyroid makes a protein called thyroglobulin that's then converted into T3 and T4. If you've already been treated for thyroid cancer and you've had a thyroidectomy, your doctor may check to make sure your cancer is gone or to see if it has come back by looking at your thyroglobulin level. Though this test can't diagnose cancer, it can be a marker for it. Since you no longer have a thyroid to make thyroglobulin, if there's more than a very low level in your blood, or if it rises after having been low, this may indicate cancer. In this case, your doctor will likely do some other tests to verify and treat you accordingly.

    Fine Needle Aspiration Biopsy

    If your doctor thinks you may have thyroid cancer, you will need to have a biopsy to tell for sure. Thyroid nodules are typically biopsied using a needle in a procedure known as fine needle aspiration (FNA) biopsy. In some cases, your doctor will begin with this test, but some doctors may do blood and imaging tests first.

    An FNA is simple, safe, and performed in your doctor's office. During an FNA, your doctor will use a needle to remove, or aspirate, cells from the nodule. To ensure the needle goes into the nodule, your doctor may use ultrasound to guide the process and will likely take a number of samples from different places in the nodule.

    Once the cells are aspirated, they are examined under a microscope by another doctor called a pathologist to determine whether the nodule is malignant (thyroid cancer) or benign. Sometimes, however, the results of an FNA are "indeterminate," meaning that it's unclear whether the nodule is cancerous or not. 

    Lobectomy

    In the case of indeterminate samples, the biopsy is usually repeated and/or genetic or molecular testing may be done. If it's indeterminate a second time, your doctor may consider a surgical biopsy or surgery to remove half of your thyroid gland, called a lobectomy. Both a surgical biopsy and a lobectomy require putting you to sleep with general anesthesia.

    In the case of the lobectomy, if you do have cancer, this is often both diagnostic and an early treatment step. However, you may eventually end up needing your entire thyroid removed, called a thyroidectomy.

    Molecular (Genetic) Testing

    Thyroid nodules are common and most are benign (non-cancerous), but determining which ones are benign and which ones are cancerous can be a tricky process. This is why researchers have created various molecular (genetic) tests that are used on cell samples obtained from a thyroid nodule. These tests help your doctor decide whether the thyroid nodule is likely cancerous or not, which often impacts whether or not you will need to have thyroid surgery. The hope is that more unnecessary surgeries can be prevented.

    One tool, called the Afirma Thyroid FNA Analysis, is a molecular diagnostic test that measures gene expression patterns within the FNA sample to make a diagnosis of either "benign" or "suspicious for malignancy." If the analysis shows the nodule to be benign, then periodic follow-up and monitoring of the nodule is typically recommended (which is usual for benign nodules). If the nodule is suspicious for malignancy, your doctor can proceed with surgery. Research suggests that the Afirma test is best for ruling out cancer, meaning it has an excellent negative predictive value.

    Other tests include the ThyGenX and ThyroSeq tests. The ThyGenX test analyzes a cell sample for gene mutations and markers to assess for the risk of cancer. This test is particularly good for ruling in cancer, so it has an excellent positive predictive value. Even more refined, the ThyroSeq test is good at both ruling in and ruling out cancer.

    If you already had an FNA biopsy that found an indeterminate thyroid nodule and your doctor is recommending a thyroidectomy, you may be interested in having another FNA done with a doctor who uses one of these molecular tests. In the end, having a more conclusive result could potentially prevent unnecessary surgery.

    Laryngoscopy

    Less commonly, if a thyroid nodule is close to your voice box, known as the larynx, a laryngoscopy may be performed to make sure it's not interfering with your vocal chords. You may also have a laryngoscopy if you're going to have surgery to remove part or all of your thyroid to see if your vocal chords are moving the way they should be. This test involves inserting a lighted flexible tube to view your larynx at high magnification.

    Imaging

    A variety of imaging tests and scans are used to help find suspicious areas that could be cancer and to see how far it might have spread. These include:

    Ultrasound

    A thyroid ultrasound can tell whether a nodule is a fluid-filled cyst or a mass of solid tissue, but it cannot determine if a nodule or lump is malignant. It can also tell how many nodules there are, as well as how big they are. As noted, ultrasound is also often used to help your doctor do a fine needle aspiration biopsy.

    Radioiodine Scan

    In this nuclear scan, also known as a radioactive iodine uptake (RAI-U) scan, you're given a radioactive tracer dose either in pill form or as an injection, followed by the scan. Nodules that absorb more radioactive iodine are more visible on the scan. These are known as "hot nodules" and are more likely to be benign. The nodules that show less radioactivity are called "cold nodules" and can be either benign or cancerous.

    By itself, this scan can't diagnose thyroid cancer, but it works especially well in the diagnosis process if your thyroid has been removed or you have high levels of TSH.

    Computed Tomography (CT) Scan

    A computed tomography (CT) scan is a specialized type of X-ray that is sometimes used to evaluate the thyroid. A CT scan can't detect smaller nodules, but it may help detect and diagnose a goiter or larger thyroid nodules. It can also help determine the size and location of any thyroid cancer and whether or not it has spread to other areas.

    Magnetic Resonance Imaging (MRI) Scan

    Similar to CT scans, an MRI can help detect enlargement in your thyroid gland, as well as tumors and tumor size. It can also be helpful in detecting the spread of tumors.

    Differential Diagnoses

    The symptoms of thyroid cancer often indicate another thyroid issue rather than cancer, so your doctor will need to rule out these other thyroid problems while looking for the disease.

    Benign Nodule

    Remember, a thyroid nodule is far more likely to be benign than cancerous. If you have a benign (non-cancerous) nodule, your doctor may decide to just keep an eye on it. This means that you'll need regular thyroid function tests and physical exams to check for any changes in how your thyroid is working. It's possible you will never need treatment at all if the nodule remains the same. If your nodule does get bigger, you will likely need another fine needle aspiration biopsy to see what's going on.

    Some doctors may start you on a medication that suppresses your thyroid from making too much hormone, such as Synthroid (levothyroxine). The point is to stop the nodule from getting any larger and perhaps even shrink it, but there isn't any clear research that this is always effective. Additionally, it may not be necessary to shrink small benign nodules that aren't causing any difficulty.

    If you're having problems breathing or swallowing, you will likely need to have the nodule surgically removed, even though it's non-cancerous. You will also need to have the nodule surgically removed if your test results come back as indeterminate or suspicious so that it can be examined for cancer.

    Goiter

    A goiter is an enlargement of your thyroid that's typically painless and may be large enough to be seen or felt. Goiters can cause problems like difficulty swallowing or breathing, coughing or hoarseness, or there may be no symptoms at all.

    They can be diagnosed using many of the same tests and procedures as listed above. Treatment for a goiter depends on how large it is and what's causing it, but may involve simply watching it, medications, surgery, or using radioactive iodine to help make it smaller.

    Hyperthyroidism

    Graves' disease is an immune system disorder that's one of the most common causes of hyperthyroidism, an overproduction of thyroid hormones. One of the main symptoms can be an enlarged thyroid, so your doctor will check you for Graves' disease using the same tests and procedures indicated for thyroid cancer diagnosis. Treatment for Graves' disease usually involves medication, radioactive iodine therapy, and potentially surgery.

    Other conditions that can cause the thyroid to produce too much hormone include toxic multinodular goiters, Plummer's disease, and toxic adenoma. These are treated the same way as Graves' disease with medication, radioactive iodine therapy, and surgery, and are diagnosed using the same tests and procedures listed above as well.

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