Molecular Testing of "Indeterminate" Cell Samples From Thyroid Nodules

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Thyroid nodules are common and most are benign (non-cancerous). But determining which ones are benign versus cancerous can be a tricky process.

This is why investigators have created various molecular tests that are used on cell samples obtained from a thyroid nodule. These tests help a doctor decide whether the thyroid nodule is likely cancerous or not, which often impacts whether or not a person undergoes thyroid surgery.

Obtaining Thyroid Cells: Fine Needle Aspiration Biopsy

The process of removing thyroid cells from a nodule, called a fine needle aspiration biopsy or FNA, is simple, safe, and performed in a doctor's office.

During an FNA, a doctor will use a needle to remove ("aspirate") cells from the nodule. To ensure the needle goes into the nodule, a doctor will use an ultrasound to guide him.

Once the cells are aspirated, they are examined under a microscope by a 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 it's unclear whether the nodule is cancerous or not. 

In the case of indeterminate samples, the biopsy is usually repeated. If it's indeterminate a second time, a doctor will consider a third biopsy or often surgery.

If a person ends up undergoing surgery and thyroid cancer is found, the thyroidectomy is considered a necessary and appropriate step in treatment.

However, when no thyroid cancer is discovered (and the nodule is benign), the patient has needlessly lost a vital organ, and in the process, become hypothyroid for life. Moreover, thyroid surgery is invasive and associated with risks like damage to your parathyroid gland and the nerve that controls your voice box 

Molecular Testing of Cells From Thyroid Nodules

With the dilemma of what to do when an FNA biopsy comes back indeterminate, researchers have begun developing tests to improve the diagnostic assessment of these questionable nodules. 

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, than the person 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 access 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 great at both "ruling in" and "ruling out" cancer.

What this may mean for your thyroid care is that if you have already had an FNA biopsy that found an indeterminate thyroid nodule, and your doctor is recommending 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 an unnecessary surgery.

A Word From Verywell

While these molecular tests are remarkable, revolutionary tests, it's important to remember that research on them is still evolving.

In other words, these tests are not perfect—doctors still need to examine each patient's unique risks and piece together how to best incorporate these diagnostic tools into their care. 


View Article Sources
  • American Thyroid Association. (2018). Fine Needle Aspiration Biopsy of Thyroid Nodules: Procedure and interpretation of results. 
  • Baca SC et al. Qualifiers of atypia in the cytologic diagnosis of thyroid nodules are associated with different Afirma gene expression classifier results and clinical outcomes. Cancer Cytopathol. 2017 May;125(5):313-22.
  • Ferris et al. American Thyroid Association Statement on Surgical Application of Molecular Profiling for Thyroid Nodules: Current Impact on Perioperative Decision Making. Thyroid. 2015 Jul 1;25(7):760-68.
  • Zhang M, Lin O. Molecular testing of thyroid nodules: A review of current available tests for fine-needle aspiration specimens. Arch Pathol Lab Med. 2016 Dec;140(12):1338-44.