MON-404 Fine Needle Aspiration of Thyroid Nodules Using the Bethesda System: An Institutional Experience at a Large Academic Center

Abstract Disclosure: S. Saad-Omer: None. M. Stan: None. M.R. Castro: None. J. Brito: None. J.E. Hallanger-Johnson: None. M.M. Ryder: None. Background: Thyroid fine needle aspiration (FNA) is a widely utilized diagnostic tool for evaluating thyroid nodules. The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) provides a standardized framework for classifying cytologic findings and guiding management. This study retrospectively reviews thyroid FNA cases at a large academic institution to analyze the distribution of Bethesda classifications.Methods: A retrospective review was conducted of all thyroid FNA cases done in the department of Endocrinology at a large academic institution performed from January 1st 2019 to October 3rd 2023. Thyroid FNA results were divided into categories according to the Bethesda classification system, such as benign, atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS), follicular neoplasm (FN), suspicious for malignancy, malignancy and non-diagnostic. FNA results that were not able to be classified were labelled as other.Results: A total of 3,291 thyroid FNA cases were included in the analysis. The distribution of cases across the Bethesda categories revealed a significant proportion of benign findings, with 73.6% classified as benign. This was followed by 8.1% follicular neoplasm, 6.56% Papillary Thyroid Cancer, 6.62% Non-diagnostic, 2.4% Atypical, and 2.3% Suspicious. 0.5% of FNA results were classified as other.Conclusion: Overall our cohort was found to have similar findings in terms of benign and confirmed PTC nodules compared to recent literature; however, the rate of atypical and non-diagnostic nodules was found to be lower. Presentation: Monday, July 14, 2025