Efficacy of Second Radioactive Iodine Therapy Based on Serum Thyroglobulin for Papillary Thyroid Cancer: A Retrospective Cohort Study

Abstract

Background: Radioactive iodine (RAI) therapy is widely used in differentiated thyroid cancer to eliminate residual cancer cells and to target metastatic lesions; however, this therapy is associated with a recurrence rate of approximately 2%. Repeat RAI therapy may be considered in patients with persistent or recurrent lesions; however, the benefits of second RAI remain unclear. In this retrospective cohort study, we evaluated the clinical impact of second RAI therapy in patients with papillary thyroid cancer (PTC) and identified potential predictors of treatment response and long-term remission.

Methods: Twenty-one patients who underwent a second round of RAI therapy for PTC were enrolled. Clinical and pathological data, including RAI dosage, second pre- and post-RAI therapy thyroglobulin (Tg) levels, post-treatment scan findings, and Tg reduction rates, were retrospectively analyzed. Treatment responses were evaluated based on changes in the second pre- and post-suppressed Tg (on-Tg) levels, and patients were grouped accordingly. Correlation and comparative analyses were performed to identify potential predictors of response and long-term outcomes.

Results: Following second RAI therapy, 11 patients (52.4%) showed a reduction in on-Tg levels, seven showed no reduction, and three were indeterminate. Higher second pre-therapy on-Tg levels, second therapy-stimulated Tg levels, and second post-therapy on-Tg levels were significantly associated with the no-response group (all P < 0.01) and correlated with the on-Tg difference rate. The indication for a second RAI (structural vs. biochemical incomplete response) and a history of reoperation also differed significantly between the groups. However, at the long-term follow-up, no clinical parameters were significantly associated with achieving no evidence of disease status.

Conclusions: Second RAI therapy was more effective in patients with structural incomplete response and in those who underwent reoperation. While second therapy Tg levels seemed to be correlated with short-term response, clinical factors and Tg levels were not predictive of long-term remission, highlighting the importance of individualized treatment planning.