Effect of thyroid nodule size on cytology reliability and incidence of malignancy: A large cohort of 1205 patients from a single center

There is controversy about whether the rates of malignancy and of false-negative malignancy are greater in large nodules. The aim of this study was to determine the reliability of cytology in ≥4cm nodules and to compare malignancy rates between ≥4cm and4cm nodules.The study included 1205 patients who underwent biopsy and subsequent thyroidectomy with the diagnosis of nodular thyroid disease between 2014 and 2019. The patients were separated into two groups, ≥4cm and4cm, according to the size of the index nodule on ultrasonography.Two hundred and eleven index nodules (17.5%) were ≥4cm. Malignancy rate on definitive pathology was 51% in4cm nodules and 30% in ≥4cm nodules. Malignancy risk was significantly lower in ≥4cm nodules than4cm nodules (P0.001). When1cm nodules were excluded and 1-4cm and ≥4cm nodules were compared, malignancy risk was also significantly lower in ≥4cm nodules (P=0.001). On definitive pathology, there were 45 false-negative results among cytologically benign nodules. There was no difference in false-negative cytology rate between4cm and ≥4cm nodules (P=0.209).The present study found no decrease in the reliability of cytology in ≥4cm nodules, and there may not be a linear relationship between nodule size and malignancy risk. Therefore, in asymptomatic cytologically benign ≥4cm nodules, surgery may not be recommended based on nodule size alone.