Purpose: The aim of this study was to evaluate the value of preablative stimulated thyroglobulin (presTg) and thyroglobulin reduction index (TRI) to predict the different responses to second radioactive iodine (RAI) therapy in differentiated thyroid cancer (DTC) patients with structural incomplete response (SIR).
Patients and Methods: A single-center retrospective study analyzed the different clinical outcomes after second RAI therapy in 206 patients with SIR. PresTg1 and presTg2 were measured before first and second RAI management and TRI was the reduction index of presTg1 and presTg2. Cut-off values of presTg and TRI were obtained using receiver operating characteristic analysis. The univariate logistic regression analysis was performed to confirm these parameters as prognostic factors to predict different responses to second RAI therapy.
Results: Only ATA risk stratification, the post-therapy whole-body scanning (Rx-WBS) findings, presTg1, presTg2, TRI, were different in patients with SIR. After second RAI therapy, 28.2% (58/206) of patients with SIR initially were reclassified as excellent response (ER). PresTg1 < 6.6 ng/mL, presTg2 < 1.2ng/mL, and TRI > 74.2% were excellent indications to predict ER from non-ER after second RAI treatment. PresTg1 > 14.9 ng/mL, presTg2 > 1.8ng/mL and TRI < 66.5% were well markers to predict poor outcome (SIR). High risk and distant metastases could still be considered as risk factors.
Conclusion: DTC patients with SIR could benefit through second RAI treatment. PresTg before each RAI therapy and TRI could be considered as effective decision-making markers for second RAI therapy and as predictive indications for clinical outcomes.
Keywords: structural incomplete response, radioactive iodine therapy, preablative stimulated thyroglobulin, thyroglobulin reduction index, differentiated thyroid carcinoma