Association between surgical extent and outcomes for low-risk 2-4 cm differentiated thyroid cancer in the 2025 ATA...

The 2025 American Thyroid Association guideline supports consideration of lobectomy (LT) for low-risk 2-4 cm differentiated thyroid cancer (DTC), but evidence on cancer-specific death (CSD) in this "gray zone" is limited. We used a population-based cohort to evaluate associations of LT versus total thyroidectomy (TT) with CSD and to develop an exploratory CSD-prediction tool.

Using SEER 2000-2022 data, we included intrathyroidal 2-4 cm N0M0 DTC treated with LT or TT without radiotherapy or chemotherapy. After 1:1 propensity-score matching, overall and cancer-specific survival were analyzed. CSD and other-cause death (OCD) were evaluated using Fine-Gray competing-risk models, and independent predictors were incorporated into a nomogram.

We identified 4192 patients and matched 1620 (810 LT; 810 TT). LT was not associated with higher overall or cancer-specific mortality. In multivariable Fine-Gray models, TT showed higher subdistribution hazard of CSD, although this association may reflect residual confounding. Subgroup analyses suggested that lower-risk scenarios-tumors 21-30 mm, unifocal disease, and no lymph-node evaluation-were associated with lower CSD with LT, whereas differences were attenuated for 31-40 mm tumors or multifocal disease. The nomogram demonstrated acceptable discrimination and calibration for exploratory CSD risk stratification.

In a strictly defined ATA-2025 low-risk 2-4 cm DTC cohort, LT was not associated with higher CSD compared with TT. The competing-risk nomogram may provide exploratory individualized risk stratification rather than direct guidance for surgical selection in this "gray-zone" population.