Background/Objectives: The 2023 revision of the Bethesda System for Reporting Thyroid Cytopathology (BSRTC) simplified the subcategorization of category III into two groups: “AUS-nuclear” and “AUS-other”. The aim of this study was to investigate the risk of malignancy (ROM) of individual BSRTC categories with a particular emphasis on the “AUS-nuclear” and “AUS-other” subcategories and to check whether the low-risk follicular-cell-derived thyroid neoplasm (LRTN) interpretation or EU-TIRADS class of the nodule modify ROM. Methods: The analysis covered the FNA results of 18,225 nodules in 12,470 patients. The rate of malignancy (the upper limit of ROM) was established on the basis of the assessment of 1660 nodules treated surgically in 978 patients. Results: In the broadest variant, with all LRTNs regarded as malignant, the ROM for subsequent categories was as follows: I: 0.4–3.5%, II: 0.1–1.3%, III: 3.8–17.7%, IV: 23.3–27.8%, V: 79.6–90.1%, and VI: 86.3–100.0%. In AUS-nuclear nodules, the ROM was 10.5–28.9%, while in AUS-other nodules, it was 2.2–12.2%. The exclusion of NIFTP or all LRTNs from cancers mainly affected the ROM of AUS-nuclear nodules: 9.4–25.9% or 8.6–23.7%, respectively. EU-TIRADS 5 class increases the ROM in AUS-nuclear nodules to 78.3%, OR: 15.7 and in AUS-other to 40.7%, OR: 6.6. Conclusions: The 2023 BSRTC is a welcome step towards simplification of the way nodules are classified within category III. The AUS-nuclear subcategory is associated with a two-times-higher incidence of malignancy than the AUS-other regardless of LRTN interpretation and EU-TIRADS class of the nodule. The EU-TIRADS 5 class of the nodule is helpful in the identification of category III nodules with a high risk of malignancy.
背景/目的：2023版甲状腺细胞病理学Bethesda报告系统（BSRTC）将III类细分为“AUS-核型”与“AUS-其他”两个亚类。本研究旨在探讨各BSRTC分类的恶性风险（ROM），重点分析“AUS-核型”与“AUS-其他”亚类的恶性风险，并验证低风险滤泡细胞源性甲状腺肿瘤（LRTN）的判读方式或结节的EU-TIRADS分级是否会影响恶性风险评估。方法：研究共纳入12,470例患者的18,225个结节细针穿刺结果。通过对978例患者手术切除的1660个结节进行病理评估，确立各分类的恶性风险率（ROM上限值）。结果：在最宽泛的评估方案中（将所有LRTN视为恶性），各分类ROM分别为：I类0.4–3.5%、II类0.1–1.3%、III类3.8–17.7%、IV类23.3–27.8%、V类79.6–90.1%、VI类86.3–100.0%。AUS-核型结节的ROM为10.5–28.9%，而AUS-其他结节为2.2–12.2%。若将NIFTP或所有LRTN从恶性肿瘤中排除，主要影响AUS-核型结节的ROM：分别降至9.4–25.9%与8.6–23.7%。EU-TIRADS 5级显著提升AUS-核型结节的ROM至78.3%（OR=15.7），AUS-其他结节ROM提升至40.7%（OR=6.6）。结论：2023版BSRTC对III类结节分类方式的简化具有积极意义。无论采用何种LRTN判读标准或结节EU-TIRADS分级，AUS-核型亚类的恶性发生率始终是AUS-其他亚类的两倍。EU-TIRADS 5分级有助于识别III类结节中具有高恶性风险的病例。
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