P10 - Revisiting the oncologic risk in toxic thyroid nodules: a retrospective cross- sectional study from a tertiary center

Introduction Toxic adenomas (TA) have traditionally been considered low risk for malignancy due to chronic suppression of TSH. As such, fine-needle aspiration biopsy (FNAB) is often avoided in these lesions. However, accumulating evidence suggests that this perceived safety may be misleading, and oncologic risk in hyperfunctioning nodules might be underrecognized. Purpose The present study aimed to determine the prevalence of thyroid malignancy in patients who underwent thyroidectomy with a preoperative diagnosis of toxic adenoma at a tertiary referral center. Methods A total of 102 patients with toxic nodular or multinodular goiter who underwent thyroidectomy at a tertiary center in Ankara, Turkey, were retrospectively analyzed. Diagnosis of a TA was based on suppressed TSH, imaging findings on Tc- 99m pertechnetate scintigraphy, and corresponding ultrasonographic confirmation. A matched control group of 101 patients with solitary, non-functioning nodules was selected based on age, sex, nodule size, and EU-TIRADS category. Preoperative and histopathological characteristics were compared between groups. Results The malignancy rate was 17.6% in the toxic group, significantly lower than the 41.6% observed in the non-toxic group (p < 0.001). Within the toxic cohort, malignancy was not associated with age, sex, TSH, or nodule size. However, malignant toxic nodules had significantly higher fT4 levels (median 1.33 vs. 0.98 ng/dL, p = 0.003) and more frequently exhibited suspicious EU-TIRADS features (p = 0.022). Among the 18 malignant toxic nodules, 77.8% were papillary, 16.7% showed capsular invasion, and 38.9% were multifocal. The mean nodule diameter was 28.3 ± 8.7 mm. At 5-year follow-up, 16 out of 18 malignant toxic nodules (88.9%) showed excellent response to treatment according to American Thyroid Association response criteria Conclusion Toxic thyroid nodules are not uniformly benign. Although the malignancy rate is lower than in non-toxic nodules, the observed 17.6% risk and presence of aggressive features support individualized evaluation. Suspicious ultrasound findings and elevated fT4 may warrant further cytological assessment, even in the presence of suppressed TSH.