Second Radioiodine Treatment: Limited Benefit for Differentiated Thyroid Cancer With Locoregional Persistent Disease

Radioactive iodine (RAI) treatment is often indicated after total thyroidectomy in differentiated thyroid cancer (DTC). However, its role in biochemical or locoregional persistent DTC is unclear. We aimed to investigate the effect of a second RAI treatment in patients with incomplete response to initial treatment and no evidence of distant metastases.Patients who underwent at least two RAI treatments over a 20-year period at a tertiary hospital were identified. Thyroglobulin levels and neck imaging were compared before and 1 to 2 years after RAI retreatment and evaluated at the last visit.The cohort included 164 patients (103 female; mean age, 46.6 ± 17 years). Of 114 patients retreated without prior reoperation, 53 had structural disease. At 1 to 2 years after RAI retreatment, 10 of the 41 patients with sufficient data had structural progression, 5 resolution/shrinkage, and 26 stable disease. Stimulated thyroglobulin (stTg) measured 93.7.1 ± 108 ng/mL before and 102.2 ± 124 ng/mL after retreatment (P = NS). The other 61 patients had biochemical-only persistence. Their stTg levels decreased from 41.9 ± 56 to 24.6 ± 54 ng/mL (P = 0.003). The 50 patients who underwent neck reoperation before RAI retreatment showed no substantial change in stTg; 21 (42%) still had imaging findings 1 to 2 years later. At final follow-up, despite additional treatment in 63/164 patients (38.4%), only 56/164 (34.1%) had no evidence of disease.This comprehensive study showed limited benefit of second RAI treatment in DTC patients with biochemical or locoregional structural persistent disease. Prospective studies are needed to distinguish patients for whom repeated RAI may be indicated to avoid unnecessary exposure.