Subclassifying "Atypia of Undetermined Significance (AUS)" Category in the 2023 Bethesda System for Thyroid Cytopathology: Analyzing K-TIRADS, BRAF V600E Mutation, and Risk of Malignancy.

The 2023 Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) update refines the atypia of undetermined significance (AUS) category by subclassifying it into AUS-nuclear atypia (AUS-N) and AUS-other atypia (AUS-O) based on risk of malignancy, to enhance clarity of diagnosis and patient management. This study evaluates the impact of AUS subclassification on malignancy risk prediction in thyroid nodules. A total of 118 AUS cases were analyzed for subclassification using the nuclear scoring (NS) system to evaluate nuclear features, along with the ultrasonography-based Korean Thyroid Imaging Reporting and Data System (K-TIRADS) for risk stratification, and BRAF V600E mutation testing.