Impact of Therapeutic Radioactive Iodine on the Recurrence of Papillary Thyroid Cancer With Extranodal Extension in Metastatic Lymph Nodes: A Propensity Score-matched Analysis

Purpose: Radioactive iodine therapy (RAI) ≥100 mCi (3.7 GBq) is commonly recommended for papillary thyroid cancer (PTC) patients with extranodal extension (ENE). However, no study has evaluated whether RAI ≥100 mCi is effective in reducing the recurrence of PTC with ENE. Methods: This retrospective cohort study enrolled 191 PTC patients with ENE who underwent total thyroidectomy and RAI. Recurrence according to RAI activity (<100 vs. ≥100 mCi) was compared before and after propensity score matching (PSM) (1:2) using Kaplan-Meier curves and Cox proportional hazards regression models. Subgroup analyses according to mass size (<4 and ≥4 cm), gender, blood vessel invasion, lymph node (LN) number (≤5 and >5), and stimulated Tg (sTg) level (<10 and ≥10 ng/mL) before and after PSM were performed. Results: During about 116 months, 5 (12.5%) and 19 (12.6%) before PSM, five (12.5%) and 3 (3.8%) after PSM recorded recurrence in <100 and ≥100 mCi groups, respectively. The impact of RAI ≥100 mCi on reducing recurrence was not significant before [log-rank P = 0.915, adjusted hazard ratio (HR) 0.49 (0.12-1.85); P = 0.294) and after PSM (log-rank P = 0.077). Subgroup analysis after PSM demonstrated the impact of RAI ≥100 mCi on lowering recurrence only in ENE patients with mass size ≥4 cm (log-rank P = 0.008), LN >5 (log-rank P = 0.007), and sTg ≥10 ng/mL (log-rank P = 0.039). Conclusions: In PTC patients with ENE, mass size ≥4 cm, LN >5, or sTg ≥10 ng/mL had a benefit from RAI ≥100 mCi compared with RAI <100 mCi.