Tiered approach to molecular testing of thyroid fine needle aspiration samples may improve preoperative diagnosis

Patients with indeterminate thyroid nodules continue to be a challenge to clinicians. Molecular testing on fine needle aspirates (FNA) is well established in the United States, but its access is limited elsewhere. We aimed to explore the utility of a pre-existing Next Generation Sequencing (NGS) platform, and the role of BRAF mutation in patient selection for preoperative molecular testing.

Patients were recruited from the Monash University Endocrine Surgery Database for BRAF immunohistochemistry status on histopathological samples; and prospectively for NGS testing of preoperative FNA samples, using the Archer DX VariantPlex (31 genes) and FusionPlex (40 genes) Comprehensive Thyroid and Lung panels.

The mean age of 90 patients (103 nodules) for NGS testing was 53, with 58 % female. Most of the nodules (n = 72, 70 %) had indeterminate cytology. Histology showed malignancy in 52 (50 %) nodules; of these, 45 had pathogenic DNA mutations and 3 had pathogenic RNA fusions on NGS testing of needle aspirates. The NGS panels were able to detect malignancy in indeterminate nodules with 75 % sensitivity, 85 % specificity, 80 % positive predictive value, and 81 % negative predictive value. 74 % of the papillary thyroid cancer population had BRAF mutations on immunohistochemistry, which showed 88 % concordance with the NGS results.

This is the first Australian study to demonstrate that pre-existing, non-proprietary NGS mutation and fusion panels can achieve high diagnostic specificity and positive predictive value for malignancy in indeterminate thyroid nodules. Furthermore, we propose exploration of using BRAF V600E testing to select patients for full NGS analysis.