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

Background: 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.

Objectives: 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.

Methods: 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.

Results: 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 ≥ 11.46 ng/mL before the second ¹³¹I treatment, primary tumor size > 2 cm, status T2 or higher, N1b status and ATA high risk.

Conclusions: 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.