MON-405 Thyroid Nodule FNA: Long-term Diagnostic Performance And Concordance With Surgical Pathology

Abstract Disclosure: Y. Ahmed: None. S.M. Saad-Omer: None. R.M. Castro: None. M. Rivera: None. M.N. Stan: None. Background: Fine-needle aspiration (FNA) is a cornerstone in the evaluation of thyroid nodules. Its accuracy during long term follow up is not well established though. Our project aims to address that. Objective: To assess long-term accuracy of FNA results at Mayo Clinic Rochester including diagnostic classifications, procedural and cytologic variables, and concordance with surgical pathology. Methods: We conducted a retrospective cohort study of patients who underwent thyroid FNA at Mayo Clinic Rochester in 2014, to allow for the long-term follow-up. Descriptive statistics summarized patient demographics, nodule characteristics, and procedural factors. Cross-tabulation was used to evaluate concordance between FNA cytology and surgical pathology. This is an interim analysis. Results: Among 199 patients (from 741 FNAs that year), the mean age was 58.6 ± 14.1 years, and 73.7% were female. The average BMI was 29.6 ± 6.4 kg/m². Most had non-toxic multinodular goiter (69.3%) or non-toxic solitary nodules (27.6%). Nodules were 45% solid, 8% cystic, and 47% mixed, with a mean size of 2.3 cm. FNA results were predominantly benign (Bethesda II, 80%), followed by malignant (Bethesda VI, 8%), suspicious for follicular neoplasm (Bethesda IV, 7.5% ), non-diagnostic (Bethesda I, 3%), and suspicious for malignancy (Bethesda V,1%). There were no cases read as Bethesda III (AUS) in 2014. Of the 16 Bethesda VI cases, 15 had surgery; 14 were confirmed malignant, and 1 was benign (Hurthle cell adenoma). Both Bethesda V cases that underwent surgery were benign. Of the 15 Bethesda IV cases, 12 had surgery; 11 were benign and 1 was malignant and 3 had long term follow up (2 benign, and one malignant based on the available data). Overall the malignancy rate for Bethesda IV was 13.3%. Surgery was performed in 12 Bethesda II cases, with final pathology available for 11; 9 were confirmed benign, while 2 were malignant. In the other 147 cases of benign FNAs that didn’t undergo surgery we have not identified any indication of necessity for surgery during the mean of 9 years of follow-up, presumably indicating their benign character. Overall malignancy rate for this group was 1.3%. We had only 6 non diagnostic FNAs (Bethesda I), with all of them during follow up proven benign (2 by surgery, 2 by repeat FNA and 2 by long term follow up). Conclusion: Long term follow up data (over 9 years) support the continued reliability of Bethesda II and VI , while conversely raising questions about the significance of the Bethesda V classification. The malignancy rate in Bethesda IV (likely including the Bethesda III category at the time) is consistent with our institutional data, although it remains lower than that reported by other institutions. We’re currently enriching our cohort to verify and strengthen our conclusions. Presentation: Monday, July 14, 2025