328 Atypia of Undetermined Significance (AUS)-Nuclear versus AUS-Other Under the 2023 Bethesda System for Reporting Thyroid Cytopathology (TBSRTC): A 15-Month Institutional Experience

Document Type

Conference Proceeding

Publication Date

3-23-2026

Publication Title

Lab Invest

Keywords

adult, aged, conference abstract, controlled study, cytopathology, diagnosis, female, fine needle aspiration biopsy, follow up, histology, histopathology, human, human tissue, major clinical study, male, middle aged, noninvasive follicular thyroid neoplasm with papillary-like nuclear features, surgery, thyroid gland, thyroid imaging reporting and data system, thyroid papillary carcinoma

Abstract

Disclosures: Kerem Ozcan: None; Gamze Gokturk Ozcan: None; Sarah Kisha: None; Lauren Gagnon: None; Lisi Yuan: None Background: AUS is a diagnostic category used for thyroid fine-needle aspiration (FNA) cases with some degree of nuclear and/or architectural atypia that do not meet criteria for Follicular Neoplasm or Suspicious for Malignancy. TBSRTC 2023 limited AUS subclassification to AUS-nuclear and AUS-other, with the former carrying a significantly higher ROM and warranting preferential molecular testing. In this study, we have evaluated clinicopathologic, radiologic and molecular features of all our AUS cases to assess if the binary subclassification effects utilization of molecular testing and clinical management. Design: We analyzed 354 thyroid FNA specimens subclassified per the 2023 TBSRTC into AUS-nuclear or AUS-other, corresponding to 347 distinct nodules from 315 patients over a 15-month period following the implementation of TBSRTC 2023. Demographic, sonographic, clinical management and molecular data were collected; molecular findings were correlated with histopathologic diagnoses when available. Results: The demographic, ultrasonographic (TI-RADS), molecular, cytologic subclassification and histopathologic outcome data are summarized in the table. AUS-nuclear comprised 23.7% (n=84) of AUS results. Molecular testing was performed on 280 nodules (80.7%), yielding benign signatures in 207 (74%) and suspicious signatures in 63 (22.5%). For suspicious cases, the reported ROM tiers were 25% (n=2), 50% (n=42), 75% (n=16) and >95% (n=1); two cases were called suspicious without an associated ROM. RAS-family alterations predominated among reportable drivers (HRAS, n=8; NRAS, n=7). Among cases with benign molecular signatures, 91% were managed with routine sonographic follow-up, six resections revealed benign histology. Among cases with suspicious molecular signatures, 29 underwent surgery with histopathologic evaluation revealing benign processes in 10, NIFTP in 10, papillary thyroid carcinoma in 9. When stratified by AUS-nuclear versus AUS-other, molecular test utilization, frequency of suspicious signatures, and malignant outcome on resection did not differ significantly (p > .05). [Formula presented] Conclusions: Although 2023 TBSRTC recognizes AUS-nuclear and AUS-other based on different ROM, in our 15-month cohort, the two subcategories did not show significant differences in clinical decision making, molecular test utilization and results, or histopathologic outcomes. Accordingly, our findings suggest that subclassification alone should not drive preferential molecular testing.

Volume

106

Issue

3

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