How innocent are thyroid nodules diagnosed with bethesda II?

Objective: Thyroidectomy is a frequently performed surgical procedure due to indications such as suspicion of malignancy, hyperthyroidism, and goiter. The frequency of this operation is increased by the endemic presence of thyroid cancer in the Eastern Black Sea region. Fine needle aspiration biopsy (FNAB) is considered the gold standard method for distinguishing between benign and malignant thyroid nodules and is critical in treatment planning. FNAB results are classified into six categories according to the Bethesda diagnostic classification, each with different treatment algorithms. According to the Bethesda classification, the malignancy risk for benign nodules is reported to be 3-7%. In our study, we aim to determine the actual malignancy rate by examining long-term follow-up data of nodules with benign FNAB results. Materials and Methods: This thesis is designed as a retrospective observational study at Karadeniz Technical University Farabi Hospital, with ethics committee approval obtained under protocol number 2021/85 on 17.03.2021. Patients who presented to the hospital between January 1, 2010, and December 31, 2023, and met the inclusion criteria were included in the study. The study criteria encompass patients over 18 years old with a "benign" FNAB result at any time. Follow-up of patients with at least one year of ultrasound follow-up and a ≥20% increase in nodule diameter or >50% increase in nodule volume, or those with malignant pathology results after surgery, were classified as "malignant." Follow-up of patients with benign biopsy results or benign surgical pathology results were classified as "benign." The study examined 28,143 biopsy procedures, evaluated 15,141 biopsy results from 9,944 patients, and analyzed follow-up data of 6,604 patients with a "benign" FNAB result at any time. Results: A total of 2,845 patients were included in the analysis, with malignancy detected in 9.4% (267 patients). The malignancy rate was found to be 9% in women and 10.8% in men. Most initial FNAB nodules were located on the right side. There were 406 patients with a history of FNAB, 293 patients with a history of non-diagnostic biopsy, and 144 patients with a history of AUS biopsy. The median follow-up duration was 26.2 months. The most common malignancy in patients with malignant outcomes was papillary thyroid v carcinoma, while most benign patients were monitored without surgery with stable ultrasound results. The most common pathology in operated benign patients was nodular goiter. Conclusion: The study evaluated malignancy rates in patients with benign FNAB results and found higher rates than reported in guidelines. However, further studies are needed to identify risk factors for malignancy in thyroid nodules with benign FNAB results. Despite the high malignancy rate in the study, 59% of patients who underwent surgery had benign results. Research is needed to prevent unnecessary surgeries in these patients. For patients undergoing FNAB due to thyroid nodules, Bethesda II was the most common result, and separate guidelines for endemic regions may be recommended for the management of these patients. Keywords: Bethesda, benign thyroid nodule, malignancy