Molecular Testing of Thyroid Nodules

Thyroid nodules are very common. Most thyroid nodules are benign, some are malignant. About 5% of adults with a thyroid nodule have thyroid cancer.

To determine which thyroid nodules are cancerous ultrasound and FNA cytology of suspicious thyroid nodules are the mainstay of investigation. About 10% of thyroid FNA’s are reported as Bethesda 3 (atypia of undetermined significance) and a further 10% are reported as Bethesda 4 (follicular neoplasm) but only about 16%-23% of these patients actually have thyroid cancer3. It is common practice however to offer patients with Bethesda 3 and 4 cytology surgery in the form of a diagnostic thyroid lobectomy (hemithyroidectomy). Although this approach detects and treats thyroid cancer in 16-23% of people in this category, 77-84% of people have an operation with no or little therapeutic benefit.

To help further determine which patients are more likely to have cancer, molecular analysis of FNA specimens can be performed. This involves testing the DNA and RNA of the cells obtained in the FNA specimens. These tests look specifically for mutations in genes associated with thyroid cancer.

In America, Thyroseq® and Affirma® are two of the common molecular tests looking at genetic mutations seen in thyroid cancers.  Using Affirma® 2/3 of patients with Bethesda 3 and 4 nodules are reclassified as benign. Similarly, Thyroseq® is able to stratify patients with Bethesda 3 and 4 nodules into low, intermediate and high risk of having thyroid cancer. Low risk patients can be observed. Thyroid surgery is recommended for intermediate and high risk thyroid nodules.

In NZ, Thyroseq® molecular analysis of FNA specimens of thyroid nodules is available but only if the FNA specimens are sent to Sullivan Nicolaides Pathology laboratory in Brisbane who in turn send it to the Sonic laboratory in New York, USA. The turnaround time is about 4 weeks. The cost to the patient is AUD $2100 (~NZD$2300, 2025 figures) and this is not covered by the patient’s health insurance.

In the near future, Idylla ThyroidPrint® molecular analysis of FNA specimens of thyroid nodules will be available in New Zealand with results available in 24 hours. 

The America Thyroid Association (ATA) guidelines recommend three options for the management of patients with Bethesda 3 thyroid nodules:

  1. Diagnostic thyroid lobectomy
  2. Close observation
  3. Molecular analysis of Bethesda 3 nodules.

The results of molecular analysis of a FNA specimen need to be taken into account alongside the history, examination findings, thyroid function tests, ultrasound findings and FNA cytology. Molecular analysis of a FNA specimen gives valuable additional information to help decide if surgery or observation of the thyroid nodule is appropriate. Observation involves annual ultrasound scans to determine any change in the thyroid nodule.

In summary, molecular analysis of thyroid nodules is a useful adjunct to ultrasound and FNA in the evaluation of thyroid nodules for malignancy. It is particularly useful in patients with indeterminate cytology (Bethesda 3 and 4) and may reduce the number of thyroid operations.

 

References:

  1. Tessler FN, Middleton WD, Grant EG, Hoang JK, Berland LL, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. (2017) Journal of the American College of Radiology : JACR. 14 (5): 587-595. doi:10.1016/j.jacr.2017.01.046 
  2. Middleton WD, Teefey SA, Reading CC, et al. Multi institutional Analysis of Thyroid Nodule Risk Stratification Using the American College of Radiology Thyroid Imaging Reporting and Data System. (2017) American Journal of Roentgenology. 208 (6): 1331-1341. doi:10.2214/AJR.16.17613
  3. Ali SZ, et al. The 2023 Bethesda System for Reporting Thyroid Cytopathology. Thyroid 2023; 33: 1039-1044. 
  4. Nasr C, et al. Real-world performance of the Affirma genomic sequencing classifier (GSC)-a meta analysis. JCEM 2022; 108: 1526-1532.
  5. Steward DL, et al. Performance of a multigene genomic classifier in thyroid nodules with indeterminate cytology. A prospective blinded multicenter study. JAMA Oncol. 2019; 5: 204-2012, doi:10.1001/jamaoncol.2018.4616. 
  6. Zafero M, et al. A thyroid genetic classifier correctly predicts benign nodules with indeterminate cytology: two independent, multicenter, prospective validation trials. Thyroid 2020; 30: 704-712.
  7. Haugen BR, et al. 2015 American thyroid association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid 2016; 26: 1-133.