Malignancy Rates in Thyroid Nodules Classified as Bethesda Categories III and IV: Retrospective Data from a Tertiary Center.

BACKGROUND: Thyroid fine needle aspiration (FNA) has a well-established role in the diagnosis of thyroid nodules, and the "Bethesda system for reporting thyroid cytopathology" is used to interpret FNA results. Bethesda categories III and IV encompass varying risks of malignancy. In addition, there is some debate in the literature about how to select among many acceptable treatment approaches.

OBJECTIVES: To establish an association between these 2 cytological categories and malignancy rates in patients treated in a referral tertiary cancer center, where surgical treatment is recommended for all these patients.

METHODS: A total of 615 thyroid nodules (582 patients) were included in this retrospective study. There were 478 nodules that were classified as Bethesda category III and 137 nodules as Bethesda category IV. Electronic records were reviewed to establish a correlation between the FNA cytological results and the final histopathological analyses. Incidentally detected carcinomas were considered separately.

RESULTS: Among the bethesda category III group, 75 malignant nodules (15.7%) were coincident with the target nodule (74 patients, 16.2%). Incidental carcinomas were found in 13.8% of these patients. The remaining 403 (84.3%) target nodules were benign. Among the bethesda category IV nodules, 23 malignant nodules (16.8%) were coincident with the target nodule. Incidental carcinomas were found in 25 patients (19.7%). The other 114 target nodules were benign. A total of 46 patients (52.3%) had carcinomas in the thyroid lobe contralateral to the one containing the target nodule, and 40 patients (45.5%) had carcinomas exclusively in the contralateral lobe.

CONCLUSIONS: We observed a 16% rate of malignancy in nodules classified as bethesda category III and 17% among bethesda category IV. When incidental carcinomas were included, the rates of malignancy doubled.