Guiding the postoperative radioactive iodine-131 therapy for patients with papillary thyroid carcinoma according to the prognostic risk groups：a SEER-based study

Purpose: The effectiveness of iodine-131( 131 I) therapy in patients with papillary thyroid cancer (PTC) of various stage is controversial. This study aimed to use prognostic risk groups to guide 131 I therapy in patients with PTC after radical thyroidectomy. Methods: : Data of 53484 patients with PTC after radical thyroidectomy were collected from the Epidemiology and End Results (SEER) database. Patients were divided into subgroups according to MACIS system and regional lymph node involvement. The prognostic role of 131 I therapy was investigated by comparing Kaplan-Meier survival analysis and Cox proportional hazard models in different subgroups. Results: : Sex, age, tumor size, invasion, regional lymph node involvement, and distant metastasis was related to the survival of patients with PTC. If MACIS<7, 131 I treatment didn’t affect the cancer-specific survival (CSS) rate. If MACIS ≥7, 131 I therapy didn’t work on CSS rate for patients with N0 or N1a<5 status; 131 I therapy had improved CSS rate for patients in the N1a≥5 or N1b status. If patients with distant metastasis, invasion, or large tumor, 131 I therapy didn’t improve CSS rate for patients in N0 or N1a<5 stage. Conclusion: After radical thyroidectomy, if MACIS<7, patients with PTC could avoid 131 I therapy. If MACIS ≥7, patients in the N0 or N1a<5 could avoid 131 I therapy; those in the N1a≥5 or N1b stage should be given 131 I therapy. Among them, all patients with distant metastasis should be given 131 I therapy.