Is second 131I treatment necessary for differentiated thyroid cancer patients and who could not benefit from it? A real-world retrospective study in China.

Abstract

The efficacy of a second radioactive iodine-131 (131I) treatment in patients with differentiated thyroid cancer (DTC) who did not achieve an excellent response (ER) following initial 131I therapy remains controversy and the population that would derive limited benefit from it is currently unclear. The aim of this retrospective study was to assess the efficacy of the second 131I treatment in DTC patients with non-ER after the initial 131I therapy, and to identify potential risk factors associated with non-benefit of the second 131I treatment. 127 DTC patients who underwent two 131I treatments following thyroidectomy were included in this study, and the therapeutic response was evaluated after each 131I treatment. Beneficial treatment was defined as an improvement in therapy response grade (e.g. from indeterminate response to ER) after the second 131I treatment, while unbeneficial treatment was defined as no change or a downgrade in therapy response grade. The potential risk factors associated with the non-benefit of the second 131I treatment were identified using univariate and multivariate logistic regression models. Following the second 131I treatment, therapy responses of 55.12% (70/127) of patients were reclassified to a better grade indicating treatment benefit, while 44.88% (57/127) showed no change or were reclassified to a worse grade suggesting no benefit from treatment. The non-benefit of the second 131I treatment was significantly associated with potential risk factors including stimulated thyroglobulin (sTg) level ≥ 11.46ng/mL before the second 131I treatment, primary tumor size > 2cm, status T2 or higher, N1b status and ATA high risk. The study results demonstrated that more than half of DTC patients could potentially benefit from a second 131I therapy. However, over 40% of patients exhibited no benefit in response to the second 131I treatment, suggesting potential overtreatment for this subgroup. Therefore, clinicians should exercise meticulous and precise decision-making based on identified risk factors when considering the necessity of a second 131I treatment.