Comparative evaluation of dynamic risk stratification according to ATA 2015 and ATA 2025 in low-risk differentiated thyroid cancer without radioiodine ablation.

PURPUSE: To compare dynamic risk stratification (DRS) according to the 2015 American Thyroid Association-Momesso et al. 2016 extension (ATA2015-M) and the 2025 ATA update in low-risk differentiated thyroid cancer (DTC) managed without radioactive iodine (I-131), and to explore the role of an intermediate thyroglobulin (Tg) cutoff of 1 ng/mL. METHODS: We conducted a retrospective analysis of a prospectively collected cohort of 74 low-risk DTC patients treated with total thyroidectomy (n = 55) or hemithyroidectomy (n = 19) between 2020 and 2024. Clinical, histopathological, and biochemical data were collected. DRS was assessed at the first follow-up visit (6 months after surgery) and at the last visit (median follow-up 27 months [IQR 16–41]) using ATA2015-M and ATA2025 criteria. An exploratory analysis applying a Tg cutoff of 1 ng/mL was performed. RESULTS: According to ATA2015-M, excellent response (ER) rates in total thyroidectomy patients increased from 49.2% at baseline to 52.8% at final follow-up. In contrast, ATA2025 classified 89.1% as ER at baseline and 98.2% at final follow-up (p < 0.001). Using the intermediate cutoff of 1 ng/mL, ER rates were 80.0% and 89.1%, respectively. Reclassification to ER under ATA2025 was primarily driven by anti-thyroglobulin antibody (TgAb) negativization, as Tg values remained stable and below the new 2.5 ng/mL threshold. No structural incomplete responses were observed. CONCLUSION: ATA2025 criteria substantially increase ER classification in low-risk DTC patients managed without I-131 compared with ATA2015-M. A 1 ng/mL Tg cutoff may provide a more realistic representation of clinical practice. The dynamic trend of TgAb, rather than their presence alone, is a key determinant for reclassification during follow-up.