Endocrine Abstracts

JOINT1845

Background: Nodules diagnosed in the atypia of undetermined significance (AUS) category represent a heterogeneous group with an indeterminate risk of malignancy. This study aimed to investigate malignancy rates in AUS subcategories and to examine the association of malignancy with cytomorphologic features in fine-needle aspiration (FNA) and ultrasonographic characteristics.

Methods: This study analyzed 196 thyroid nodules with AUS cytology that underwent surgical resection, Among these, 176 nodules were classified as AUS-Nuclear (AUS-N), while 20 were categorized as AUS-Other (AUS-O). Cytomorphological and ultrasonographic features, along with the American College of Radiology Thyroid Imaging Reporting and Data System (ACR-TIRADS) and the European Thyroid Imaging Reporting and Data System (EU-TIRADS) classifications, were analyzed to assess the association between malignancy and AUS subcategories.

Results: Risk of malignancy (ROM) for AUS nodules was determined to be 19,4% (21% for AUS-N and 5% for AUS-O, P = 0,132). We observed that malignancy was more frequently associated with nodules of smaller maximum diameter (P = 0.003). A significantly higher ROM was observed in nodules with an oval shape, solid composition, hypoechogenicity, irregular margin and microcalcification (Odds Ratio (OR): 5,83, 2,24, 2,31, 9,75 and 3,34 respectively). The presence of irregular margins was found to independently increase the risk of malignancy by 6,53-fold, regardless of other sonographic features. A statistically significant difference in ROM was observed across ACR and EU-TIRADS categories within the AUS nodules (P = 0.005 and 0.003, respectively) and the AUS-N group (P = 0.001 and P = 0.002, respectively). In the AUS-O group, no significant results were observed for either system (P = 0.3 for both). A marked increase in ROM was observed with nuclear enlargement, overlapping, hyperchromasia, and pseudoinclusions (OR: 3.33, 2.17, 3.31, and 4.55, respectively), while oncocytic atypia was associated with a reduced risk (OR: 0.44). The presence of pseudoinclusion and nuclear overlapping were found to significantly increase malignancy risk independently of other factors (OR:7,99 and 5,50 respectively). Repeat AUS FNAs (P = 0.07), were found to significantly increase the ROM.

Conclusion: We found that the ROM in AUS nodules, particularly in the AUS-N category, were higher than those reported in the literature. We established an association between cytomorphologic features and malignancy. To the best of our knowledge, we are the first to report an increased malignancy risk linked to nuclear hyperchromasia in AUS nodules and the association between ACR-TIRADS and the AUS-N subcategory.