Patient Redistribution Across Risk Categories in Differentiated Thyroid Cancer Using the 2025 Versus 2015 American Thyroid Association Risk Stratification Systems.

OBJECTIVE: The 2025 American Thyroid Association (ATA) guidelines for differentiated thyroid cancer (DTC) expanded and refined the risk stratification system (RSS). The extent of patient redistribution across risk categories and the clinicopathologic drivers of reclassification remain unclear. METHODS: We conducted a retrospective study of adult DTC patients who underwent thyroid surgery at a tertiary cancer center between 1999 and 2025. The 2015 and 2025 ATA RSS criteria were applied to the same cohort using R-based algorithms. Patient migration across risk categories and clinicopathologic factors associated with reclassification were analyzed descriptively. RESULTS: A total of 843 patients with DTC (papillary, follicular, oncocytic, high grade, poorly differentiated) were included in the study. Most patients with DTC (669; 79.4%) remained in the same risk category, while 174 (20.6%) migrated to a different one. Among 2015 ATA low-risk patients, 105 (12.6%) were reclassified to higher-risk categories by the 2025 ATA RSS, including 84 to the low-intermediate group and 21 to the intermediate-high group. Additionally, 69 patients (8.2%) were reclassified from the 2015 intermediate-risk category to the 2025 high-risk category. Consequently, under the 2025 ATA RSS, the proportion of low-risk patients decreased by 29.7%, whereas the 2025 ATA intermediate-risk (low-intermediate and intermediate-high) and high-risk groups increased by 9.6% and 8.2%, respectively. No downward reclassification was observed. CONCLUSION: Application of the 2025 ATA RSS resulted in upward reclassification. The clinical implications of this redistribution remain to be validated, and further work is needed to correlate the revised risk categories with recurrence rates and disease-specific outcomes.