Risk of malignancy and necessity of completion thyroidectomy in patients with indeterminate thyroid nodules (Bethesda III and IV), more than expected in endemic region

American Thyroid Association (ATA) argues that the prevalence of malignancy of the indeterminate nodules may vary substantially among regions, and states that it is crucial to know the prevalence of malignancy within each indeterminate cytological category at one's institution. Our aim is to draw attention to the malignancy rates of indeterminate nodules that cannot be underestimated in an endemic region and raise awareness to differences across different populations. Between March-2021 and June-2024, 13,531 fine needle aspirations were performed on thyroid nodules in a single institution. Of these 2121 nodules were classified as indeterminate (Bethesda III-IV) and 242 patients underwent surgery. Demographic characteristics, nodule size, risk of malignancy, tumor types and subtypes were evaluated. The necessity of radioactive iodine (RAI) therapy and consequent completion thyroidectomy was investigated. Of the 242 patients 123 (50.8%) underwent lobectomy and 119 (49.2%) underwent total thyroidectomy. In total, 115 (47.5%) of 242 patients resulted in malignancy (186 patients were Bethesda-III and 82 (44.1%) of them were malignant; 56 were Bethesda-IV and 33 (58.9%) of them were malignant). Incidental carcinoma was detected in a different focus other than the indeterminate nodule in 17 patients. RAI therapy was indicated in 39 patients (33.9%) primarily based on the ATA guideline, and 24 (20.8%) patients who initially underwent lobectomy required completion thyroidectomy. Risk of malignancy in indeterminate thyroid nodules varies endemically. Each region should know their own risk and each patient's treatment should be tailored accordingly. In this way, under-overtreatment and related morbidities will be prevented.