Multicenter analysis of radioactive iodine therapy outcomes after total thyroidectomy for T1-T2 stage papillary thyroid carcinoma with cervical lymph node metastasis in China.

[BACKGROUND] The optimal approach for radioactive iodine (RAI) therapy of T1-T2 stage papillary thyroid carcinoma (PTC) with cervical lymph node metastasis following total thyroidectomy (TT) remains unclear. This study aimed to provide individualized RAI therapy recommendations regarding the type of therapy, frequency, dosage, and interval after surgery based on treatment response.

[METHODS] This multicenter study enrolled 408 T1-T2 PTC patients with cervical lymph node metastasis who underwent TT. Data were derived from a collaborative initiative involving major thyroid cancer centers across China, which prospectively standardized clinical data collection for differentiated thyroid carcinoma between 2015 and 2022. Propensity score matching (PSM) was employed to balance baseline characteristics between the TT + RAI therapy group and the TT group. Comparisons of clinical-pathological parameters were performed before and after PSM. Primary endpoints included structural incomplete response (SIR) and biochemical incomplete response (BIR). Variables with statistical significance ( P < 0.05) or clinical relevance in univariate analysis were subjected to multivariate Cox regression. Recurrence-free survival (RFS) was analyzed using Kaplan-Meier methods with log-rank testing.

[RESULTS] Among the cohort, 280 patients (68.6%) underwent RAI therapy following TT. During a median follow-up of 76.8 months, 41 patients (10.0%) demonstrated incomplete responses, comprising SIR ( n = 18) and BIR ( n = 23). After PSM, 28 patients (12.0%) exhibited incomplete responses (SIR: 13 and BIR: 15). Comparative analysis revealed no statistically significant differences in SIR/BIR rates between the TT + RAI cohort and TT group ( P > 0.05). Cox regression analysis identified the lymph node metastasis ratio as an independent predictor of SIR development (hazard ratio [HR] 5.130; 95% confidence interval [CI]: 1.194-22.051; P = 0.028). Kaplan-Meier survival curves demonstrated comparable outcomes between groups for both structural recurrence-free survival (RFS structural ) and biochemical recurrence-free survival (RFS biochemical ).

[CONCLUSION] In T1-T2 PTC with cervical lymph node metastasis, no significant difference was observed in the SIR or BIR between TT + RAI and TT groups. The frequency, dose, and interval of RAI therapy after surgery were not considered risk factors for SIR or BIR.