Molecular Testing of Thyroid Samples

Discovering a thyroid lump on yourself may mean you need to find out if the lump is benign or malignant (cancerous). These lumps, called thyroid nodules, are quite common. Finding a thyroid nodule can seem scary, but the presence of a nodule doesn’t automatically mean it’s cancer. A fine needle aspiration (FNA) is the best way to determine whether the nodule is truly, cancerous. Oftentimes, the diagnosis is not clear cut. The usage of new molecular tests can help provide a clear diagnosis.

About Thyroid Cancer

Most thyroid cancers are not fatal. As many as a quarter of all autopsies show incidental thyroid cancers that had never been detected while the patient was alive. The most common of these are papillary thyroid carcinoma and follicular carcinoma, which have very good prognoses. However, a few types of thyroid cancer are more dangerous, such as medullary thyroid cancer, poorly differentiated thyroid cancer, and anaplastic thyroid cancer. An FNA is the standard of care in order to obtain a specimen for testing. An FNA is quick and simple. The test can be performed in an outpatient setting and the results are usually available soon thereafter.

What is Molecular Testing?

After an FNA biopsy, the sample is processed by the lab and viewed by a cytopathologist. If the sample results are not clearly malignant or benign (also known as an indeterminate nodule, which is different from a non-diagnostic sample where there isn’t enough material to even make a diagnosis), then further molecular tests can be done to clarify the diagnosis. As much as 20% of FNA biopsies are found to be indeterminate.
Many people with indeterminate thyroid nodules end up going through diagnostic surgeries, and these surgeries are often unnecessary because over 60% of these cases don’t have cancer.  However, with these new molecular tests, the nodules originally deemed indeterminate can be more accurately distinguished as either cancerous or benign. Therefore, these tests help reduce the need for diagnostic surgery.
Molecular testing is a technique that examines proteins in the cells such as RNA and DNA. Three of the newest molecular tests for thyroid cancer are Afirma, ThyroSeq v2 and ThyGenX. These tests look for what are called molecular markers in the cells obtained from an FNA biopsy by a fine needle aspiration specialist.
Each of these three new molecular tests has different advantages depending on what the doctor is trying to rule out or or rule in. Each test differs in their cost, accuracy, and effectiveness for different cell and genetic patterns. The choice of test should be discussed with your doctor.