25 Diagnostic utility of molecular and imaging biomarkers 2 Table 1. Overview of classification systems for thyroid cytology Bethesda System for the Reporting of Thyroid Cytology [26, 44] British Thyroid Association (BTA) [45] SIAPEC-IAP (Italy) [46] Category Description Category Description Category Description Malignancy rate [26, 44] Proposed management (2015 ATA guidelines [17]) I Nondiagnostic / unsatisfactory Thy1 Thy1c Nondiagnostic Nondiagnostic Cystic lesion TIR1 TIR1c Nondiagnostic Nondiagnostic-cystic 1%-4% Repeat FNAC with US guidance II Benign Thy2 Thy2c Nonneoplastic Nonneoplastic Cystic lesion TIR2 Nonmalignant / benign 0%-3% No clinical follow-up or treatment required III Atypia of undetermined significance / follicular lesion of undetermined significance (AUS/FLUS) Thy3a Atypical features present TIR3a Low-risk indeterminate lesion ~5%-15% Repeat FNAC. If second Bethesda III result, consider additional tests and/or diagnostic hemithyroidectomy IV Follicular neoplasm / suspicious of a follicular neoplasm, including Hürthle cell (oncocytic) type Thy3f Suspicious of follicular neoplasm TIR3b High-risk indeterminate lesion 15%-30% Consider additional tests and/or diagnostic hemithyroidectomy V Suspicious of malignancy Thy4 Suspicious of malignancy TIR4 Suspicious of malignancy 60%-75% Thyroid surgery recommended. Consider preoperative additional (molecular) testing to determine extent of surgery VI Malignant Thy5 Malignant TIR5 Malignant 97%-99% Thyroid surgery recommended
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