Reassessing false-negative rate and size cutoff for papillary thyroid cancer with fine-needle aspiration in thyroid nodules.

[BACKGROUND] Fine-needle aspiration is the primary diagnostic tool for malignancy in thyroid nodules. However, fine-needle aspiration of larger nodules may yield greater false-negative rates for thyroid cancer. This study evaluates the performance of fine-needle aspiration in the diagnosis of papillary thyroid cancer across various thyroid nodule sizes.

[METHODS] A retrospective study was conducted using prospectively collected data from 2,525 patients who underwent initial fine-needle aspiration and thyroidectomy between 2008 and 2022 at a single tertiary institution. Patients aged ≥18 years with Bethesda category II or VI thyroid nodules by fine-needle aspiration and a final histopathologic diagnosis of papillary thyroid cancer were included. Thyroid nodules were stratified by size: <1 cm, 1.0-1.99 cm, 2.0-2.99 cm, 3.0-3.99 cm, and ≥4.0 cm. Final histopathology was correlated with preoperative fine-needle aspiration Bethesda II and VI results. Statistical analysis was performed using analysis of variance and post-hoc testing.

[RESULTS] A total of 753 patients were included in the analysis: 634 women (84.2%) and 119 men (15.8%), with a mean age of 49 years. Sensitivity, specificity, positive predictive value, negative predictive value, false positive, and false negative rates for fine-needle aspiration were 84.8%, 96.5%, 96.8%, 83.9%, 3.4%, and 15.2%, respectively. False-negative rates increased with thyroid nodule size: 3.4% (n = 2) for nodules <1 cm, 4.9% (n = 8) for 1.0-1.99 cm, 16.2% (n = 18) for 2.0-2.99 cm, 46.4% (n = 26) for 3.0-3.99 cm, and 46.2% (n = 12) for nodules ≥4.0 cm. Significant differences in false-negative rates were observed for nodules ≥3.0 cm (P < .001). Post-hoc testing revealed a significant difference between the ≥3 cm and <3 cm groups. No significant difference was found between nodules of 3.0-3.99 cm and ≥4.0 cm.

[CONCLUSION] Although a thyroid nodule size >4 cm is traditionally considered an indication for thyroidectomy, this study demonstrates an increased incidence of false-negative results for PTC with thyroid nodules ≥3 cm. Future studies are needed to validate these findings.