335 Prevalence of Atypia of Undetermined Significance (AUS) in Thyroid Fine Needle Aspirations Before and After Implementation of the 2023 Bethesda System for Reporting Thyroid Cytopathology

Document Type

Conference Proceeding

Publication Date

3-24-2025

Publication Title

Lab Invest

Keywords

adolescent, cancer risk, conference abstract, controlled study, cytology, cytopathology, diagnosis, fine needle aspiration biopsy, human, major clinical study, male, prevalence, quality control, reproducibility, retrospective study, thyroid gland

Abstract

Disclosures: Gamze Gokturk Ozcan: None; Lauren Gagnon: None; Nazila Azordegan: None; Ziying Zhang: None; Lisi Yuan: None Background: The 2023 Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) now subclassifies atypia of undetermined significance (AUS) into nuclear atypia (AUS-nuclear) and non-nuclear (AUS-other) subcategories. As a heterogeneous category of TBSRTC, the AUS rate varies greatly among different laboratories (from 1% to over 20%) and has at best only fair reproducibility. The recommendation about the upper limit of the AUS diagnostic category to no more than 10% of thyroid FNAs in the 2017 edition of TBSRTC continues unchanged. A suggestion about AUS:malignant ratio ≤ 3.0 as a laboratory quality control was included in the 2023 edition. The new subclassification of AUS into nuclear and other is designed to improve reproducibility and to better reflect the risk of malignancy and subsequent management. Design: At our institution, the 2023 TBSRTC was implemented in September 2023. A retrospective review of thyroid FNAs from our center from January 2020 to August 2024 was performed. Results were stratified by year and an annual rate and overall rate of AUS over a four-year period before the implementation of the 2023 TBSRTC and one-year period after the implementation were calculated. The inclusion criteria was any diagnosis of atypical, AUS, or follicular lesions of undetermined significance (FLUS) before September 2023, and AUS-nuclear, AUS-other afterwards. Results: Among 4662 cases of thyroid FNA cytology performed in our institution from January 2020 to August 2023, 755 cases were diagnosed as atypical. The overall rate of AUS in this four-year period was 16.2%. The annual rate of AUS had increased from 10.3% to 24.7%. After the implementation of 2023 TBSRTC in September 2023 (one-year period 9/2023-8/2024), the annual rate of AUS has decreased to 19.7%. The AUS/malignant (A/M) ratio was 4.74 in 2023 before the implementation of 2023 TBSRTC; the A/M ratio decreased to 2.98 in the one-year period afterwards. [Formula presented] Conclusions: In the present study AUS rate is 19.7% after the implementation of the 2023 TBSRTC. It is higher than the recommended upper limit, but the 2023 TBSRTC appeared helpful in reducing AUS rate in our institution. AUS/malignant ratio is a useful quality measure and our A/M ratio of 2.98 was within the recommended range of ≤ 3. Reporting AUS results and AUS/malignant ratio as we have done could potentially establish the acceptable range of AUS within an institution and limit AUS interpretations.

Volume

105

Issue

3

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