Prognostic Implications of the Bethesda System in Fine-Needle Aspiration for Follicular Thyroid Carcinoma

CONTEXT.—: Fine-needle aspiration is an effective tool for sampling thyroid nodules; its results are classified according to the Bethesda System for Reporting Thyroid Cytopathology (BSRTC), whose categories define malignancy risks. OBJECTIVE.—: To compare the histologic outcomes and disease-free survival (DFS) with the preceding BSRTC categories, we hypothesized that the initial cytologic categories may reflect long-term outcomes in follicular thyroid carcinoma (FTC), similar to those observed in papillary thyroid carcinoma. DESIGN.—: This retrospective study enrolled 134 patients with FTC who underwent preoperative cytology between April 2011 and December 2020. Results were classified into 6 categories according to the BSRTC: nondiagnostic, benign, atypia of uncertain significance (AUS), follicular neoplasm (FN), suspicious for malignancy, or malignant. RESULTS.—: Overall, 8 of 134 patients (6.0%) were categorized as having a nondiagnostic FTC, 35 of 134 (26.1%) as benign, 51 of 134 (38.1%) as AUS, and 40 of 134 (29.9%) as FN. No lesions were classified as suspicious for malignancy or malignant. The nondiagnostic, AUS, and FN categories were associated with a progressively higher risk of vascular invasion, disease recurrence, and high-risk FTC, based on the 2022 World Health Organization classification (P for trend = .01, .01, and .01, respectively). Disease-free survival was lower in the FN group (log-rank P = .01). CONCLUSIONS.—: The initial BSRTC results may reflect not only the risk of malignancy but also the presence of vascular invasion and poor prognosis when the thyroid nodule is diagnosed as FTC. These results may provide prognostic information for therapeutic decision-making and clinical management of FTC.