Evaluating local thyroid cytopathology practices by molecular quality metrics: A multi-institutional study on 4651 FNAs with a focus on the role of the interventional cytopathologist.

Background: The diagnostic accuracy of thyroid fine-needle aspiration (FNA) can be highly influenced by the technical skills of the operator performing the procedure and by interobserver variability in microscopic interpretation. This is particularly true for the indeterminate categories. Recently, molecular testing has been proposed as an ancillary tool for monitoring the performance of different thyroid cytopathology practices. The objective of this multicenter study was to evaluate the quality of different local cytopathology practices by assessing the impact of interventional cytopathologists on FNA adequacy for molecular testing and the variations in mutation rates across different health care centers operating in the Campania region.

Methods: The study included 4651 thyroid FNA samples diagnosed in different Southern Italian clinical laboratories belonging to the TIRNET (the Tiroide Network). FNA samples were collected by different proceduralists and were classified by local cytopathologists according to The Bethesda System for Reporting Thyroid Cytopathology. FNAs classified as atypia of undetermined significance, follicular neoplasm, suspicious for malignancy, and malignant were centralized for a real-time polymerase chain reaction-based, seven-gene test at the authors' institution.

Results: Centers that employed interventional cytopathologists obtained fewer unsatisfactory FNA samples for molecular testing (11.3%) than centers that employed noncytopathologists (16.7%; p < .05). Furthermore, a significant variation in the mutation rate was observed in FNAs diagnosed by different local cytopathologists; indeterminate categories had the highest percentage of mutation rate variability among centers.

Conclusions: Interventional cytopathologists obtained higher yields of diagnostic material for molecular testing. Finally, the current results suggest that the variability in mutation rates among different centers may highlight the low reproducibility of microscopic criteria among cytopathologists, particularly for indeterminate cases.