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

OBJECTIVE: 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 and<4cm nodules. METHODS: 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 and<4cm, according to the size of the index nodule on ultrasonography. RESULTS: Two hundred and eleven index nodules (17.5%) were ≥4cm. Malignancy rate on definitive pathology was 51% in<4cm nodules and 30% in ≥4cm nodules. Malignancy risk was significantly lower in ≥4cm nodules than <4cm nodules (P<0.001). When<1cm 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 between<4cm and ≥4cm nodules (P=0.209). CONCLUSION: 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.