Validation of the 2025 ATA risk stratification system in a cohort of patients with papillary thyroid carcinoma

CONTEXT: The updated risk stratification system for papillary thyroid cancer (PTC) introduced by the 2025 American Thyroid Association (ATA) guidelines has not yet been validated in a real-world setting. DESIGN: Retrospective observational study. SETTING: Tertiary care center. PATIENTS: Data from 670 PTC patients with complete histopathological and final disease outcome were included. MAIN OUTCOME MEASURES: We evaluated how patients previously classified by the 2015 ATA risk stratification system are redistributed according to the updated version and assessed the impact of reclassification on final disease outcome prediction. RESULTS: The reclassification according to the 2025 ATA risk stratification showed that the proportion of "low-risk" PTC decreased by 22.2%, while "intermediate-risk" and "high-risk" PTC increased by 41.7 and 14.9%, respectively. Cross-comparison between the two stratification systems revealed that structural disease persistence in the 2025 "low-risk" and "high-risk" classes was comparable. The 2025 "intermediate-high-risk" class was similar to the former "intermediate-risk" class, whereas the "low-intermediate-risk" class emerged as a new class, with a risk of structural disease persistence higher than that of the 2015 "low-risk" class (p = 0.003), but lower than that of the 2015 "intermediate-risk" class (p = 0.012). CONCLUSIONS: In a real-life context, the 2025 ATA risk stratification system led to a shift toward higher-risk classes. The newly defined "low-intermediate-risk" class was the only class that significantly diverged from the classes of the 2015 stratification, with a risk of structural recurrence between the prior "low-risk" and "intermediate-risk" classes, highlighting the need for dedicated prospective studies to address proper management of this newly-defined group of patients.