AUS in Thyroid Cytology: A 21-Year Institutional Experience and the Impact of Atypia Subclassification
Diagnostic Cytopathology, 2026 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Publication Date: 2026
- Doi Number: 10.1002/dc.70149
- Journal Name: Diagnostic Cytopathology
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, BIOSIS, EMBASE, MEDLINE, Biomedical Reference Collection: Corporate Edition (EBSCO), Health Research Premium Collection (ProQuest)
- Keywords: atypia of undetermined significance, AUS-nuclear, AUS-other, FNA, risk of malignancy—ROM, thyroid
- Hacettepe University Affiliated: Yes
Abstract
Background: The Atypia of Undetermined Significance (AUS) category remains one of the most controversial groups in The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). We aimed to assess AUS outcomes at our institution over a 21-year period. Methods: Thyroid fine needle aspiration (FNA) cases between 2000 and 2021 were retrospectively reviewed, and AUS diagnoses were identified. Cases were subclassified as nuclear (AUS-N) or other atypia (AUS-O). The AUS rates per year and cytopathologist, risk of malignancy (ROM), and radiological features were analyzed. Results: There were 15,099 thyroid FNAs, of which 553 initial AUS cases were included. The AUS rate was 0.7% and 6.6% before and after the implementation of the TBSRTC. AUS rates among cytopathologists ranged from 2.8% to 8.8%. Of the 553 cases, 168 (30%) underwent surgery, 269 (48.6%) had a repeat FNA, and 116 (20.9%) were observed or lost to follow-up. Pre-TBSRTC the overall ROM was 20%, and post-TBSRTC 30.1% and 26.7% when NIFTP was considered malignant, and nonmalignant, respectively. ROM was significantly higher in AUS-N than AUS-O (39% vs. 20.7% with NIFTP malignant; 36% vs. 17.6% without; p < 0.01). ROM did not differ significantly between patients with one or two consecutive AUS diagnoses (26.7% vs. 25%). On ultrasonographic findings, calcifications, and cystic changes were more frequent in AUS-N, while nodule size and multiplicity were similar between groups. Conclusion: In conclusion, AUS-N and AUS-O demonstrated significantly different ROMs, supporting the 2023 TBSRTC subclassification. Repeat FNA led to diagnostic reclassification in a substantial proportion of cases, supporting its role as an acceptable management strategy, particularly in settings with limited access to molecular testing.