Prognostic Factor Analysis for Risk-Stratified Papillary Thyroid Carcinoma and Nomogram Development for Predicting Structural Incomplete Response to Radioactive Iodine Therapy in Intermediate-Risk Patients.

BACKGROUND: Structural incomplete response (SIR) after radioactive iodine (RAI) therapy indicates persistent or recurrent structural disease and has important implications for the long-term management of patients with papillary thyroid carcinoma (PTC). However, predictors of SIR across recurrence-risk strata remain incompletely characterized. AIMS: To identify factors associated with SIR following RAI therapy in risk-stratified PTC patients and to develop a predictive nomogram for intermediate-risk patients. METHODS AND RESULTS: We retrospectively analyzed 615 PTC patients who underwent thyroidectomy, lymph-node dissection, and 131I therapy. Patients were re-stratified according to the 2025 American Thyroid Association recurrence-risk framework into a low/low-to-intermediate-risk group and an intermediate-high/high-risk group. In 396 intermediate-risk patients with lymph-node metastasis, univariable and multivariable logistic regression analyses were used to identify independent predictors of SIR, and a nomogram was developed and internally validated. SIR rates differed significantly between risk groups (p < 0.001). Stimulated thyroglobulin (sTg) independently predicted SIR across all risk strata. The number of lymph-node metastases (LNM) and lymph-node yield additionally predicted SIR in intermediate-high/high-risk patients. In intermediate-risk patients, age, tumor size, lymph-node ratio, sTg, and LNM were independent predictors of SIR. The nomogram yielded an area under the curve of 0.865 (95% CI, 0.814-0.916) in the training cohort and 0.733 (95% CI, 0.617-0.849) in the internal hold-out validation cohort; the bootstrap optimism-corrected area under the curve was 0.853, and the optimism-corrected calibration slope was 0.92. CONCLUSION: sTg and LNM are key predictors of SIR in risk-stratified PTC patients. In this single-center retrospective cohort, the nomogram showed good discrimination and calibration for SIR in intermediate-risk patients; external multicenter validation is warranted before clinical application.