Molecular Testing of Thyroid Fine-Needle Aspirations Improves Presurgical Diagnosis and Supports the Histologic Identification of Minimally Invasive Follicular Thyroid Carcinomas

Abstract

Molecular testing of air-dried FNA samples improves presurgical diagnosis. Discrepant sensitivities and specificities reported previously are most likely related to the use of different grading schemes resulting in different compositions of the cytologic categories, interobserver variability to diagnose follicular variant of papillary thyroid carcinomas and a different prevalence of RAS mutations in follicular carcinomas. The knowledge of the molecular testing might support the histologic identification of minimally invasive follicular carcinomas.

DIAGNOSIS OF ENDOCRINE DISEASE: High-yield thyroid fine-needle aspiration cytology: an update focused on ancillary techniques improving its accuracy

“…Actually, several authors have demonstrated the feasibility of molecular testing (including NGS) in routine thyroid FNA using air-dried, spray-fixed, ethanol-fixed smears, or even liquid-based cytology (LBC) material preserved in alcoholic fixative solution (33,34,35).…”

“…From these data, a malignancy risk stratification of patients with an AUS/FLUS and FN/SFN diagnosis can be evaluated to decide whether or not surgery is indicated (36). The gain in sensitivity attributable to the application of molecular tests to FNA material is around 20%, reaching 80% as opposed to 60% with cytological analysis alone (35). We should be aware that the main disadvantage of the application of molecular mutational tests to thyroid FNA remains the fact that 30-40% of thyroid cancers do not harbor known mutations.…”

European Thyroid Association Guidelines regarding Thyroid Nodule Molecular Fine-Needle Aspiration Cytology Diagnostics

“…Formalin fixation leads to the crosslinking of nucleic acids and proteins, fragmentation of isolated nucleic acid material, and the possibility of sequence alterations. This point needs to be considered when other sources of samples such as cell block or cytology preparation with preserving liquid are used and specific protocols have to be applied in order to obtain high-quality nucleic acid isolation [16] Different types of specimen obtained from thyroid FNA procedure may be used for molecular analysis: (a) cells collected from FNA during the procedure [11], (b) cells retrieved from FNA-stained smears [1], (c) cells retrieved from air-dried slides [17], and (d) paraffin sections from cell blocks. All these samples have been shown to be suitable for point mutation analysis as well as for detecting chromosome rearrangements [17].…”

“…Nucleic acid recovering from direct smears offers relevant advantages: first, it permits to check the cells before nucleic acid isolation, allowing the analysis of exactly those cells that are cytologically indeterminate and the enrichment of the pathological population [16, 17]. This is not possible if a dedicated pass of FNA is washed in a tube containing nucleic acid preservative solution.…”

“…Tumor enrichment mitigates the error based on the possibility that tumors may be heterogeneous with respect to a specific molecular alteration. Second, molecular tests from direct smears are performed on the already available diagnostic material without additional reaspiration of the nodule, patient discomfort, and the risk of inadequate sampling due to recent intranodular hemorrhage [16, 17]. …”