Evaluation of the Necessity of Repeat Biopsy in Patients with Thyroid Nodules Classified as Atypia of Undetermined Significance (AUS) Based on Fine-Needle Aspiration Biopsy Results

<i>Background and Objectives:</i> The necessity of repeat fine-needle aspiration biopsy (FNAB) in nodules diagnosed as atypia of undetermined significance (AUS) remains debated. This study evaluates the role of a second FNAB in surgical decision making. <i>Materials and Methods:</i> A retrospective analysis was conducted on 131 patients (105 females and 26 males) who underwent surgery following an AUS diagnosis between 2020 and 2024. Patients were grouped based on whether surgery was performed after the first or second FNAB. Demographics, pathology, and ultrasound findings were compared. <i>Results</i>: Of the patients, 66 (50.7%) underwent surgery after the first FNAB and 65 (50.3%) after a second AUS diagnosis. Malignancy was detected in 47 out of 66 (71.2%) patients in the single biopsy group and in 44 out of 65 (67.7%) patients in the repeat biopsy group (<i>p</i> = 0.804). T1a tumors were more frequent in the first FNAB group (63.8% vs. 37.2%, <i>p</i> = 0.021). The EU-TIRADS classifications showed no significant differences. <i>Conclusions</i>: The malignancy rate observed (71.2%) exceeds reported rates in the literature, suggesting regional variability. Early-stage cancers were more frequent in patients operated on after the first FNAB, questioning the necessity of repeat biopsy and indicating a potential need to revise current guidelines.