Effective Use of microRNA, BRAF and Sonographic Risk Assessment in Bethesda III Thyroid Nodules Requires a Different Approach to Nodules with Features of Nuclear Atypia and Other Types of Atypia

SIMPLE SUMMARY: Commercially available molecular tests for thyroid fine needle aspiration biopsy are expensive and usually require an additional aspiration of the nodule. Therefore, we checked whether a method free of these main disadvantages would be feasible in the case of Bethesda category III nodules. To this end, we decided to use the material remaining in the needle after preparation of the classic smear and to limit molecular diagnostics to a few well-recognized tests: BRAF V600E mutation and three microRNAs, miR-146b, miR-221 and miR-222. At the same time, we assessed the potential of the combined ultrasound and molecular evaluation of nodules and considered the distinctiveness of two main subcategories of Bethesda category III: nodules with nuclear atypia and nodules with other types of atypia (predominantly architectural). As we show, this approach facilitates clinical decision making for both of these subcategories and prevents a significant number of diagnostic thyroid surgeries. ABSTRACT: The aim of the study was to analyze the diagnostic usefulness of the combined assessment of the ultrasound risk category of the nodule (evaluated with EU-TIRADS system), the presence of BRAF V600E mutation and the expression of selected microRNAs (miR-146b, miR-221 and miR-222) in Bethesda category III thyroid nodules, separately for cases with nuclear atypia (AUS-nuclear) and cases with other types of atypia (AUS-other). We evaluated 161 nodules (66 AUS-nuclear and 95 AUS-other) with known results of postoperative histopathological examination. The rate of cancer and the rate of PTC among cancers were nearly three times higher in the AUS-nuclear than the AUS-other group. For AUS-nuclear nodules, the most effective diagnostic panel included, in addition to repeat FNA, the assessment of BRAF V600E mutation and the expression of miR-146b and miR-222 (sensitivity: 93.5%, specificity: 80.0%). For AUS-other nodules, a two-step procedure was most effective: at the first stage, forgoing surgical treatment in subjects with a benign repeat FNA outcome, and, at the second stage, the assessment of miR-222 expression and the EU-TIRADS category (sensitivity: 92.3%, specificity: 76.8%). The optimal use of molecular methods in the diagnostics of category III thyroid nodules requires a separate approach for nodules with nuclear atypia and nodules with other types of atypia.