Characterization of the patient profile and efficacy of empirical radioiodine therapy in differentiated thyroid cancer with biochemical evidence without identified iodine-avid structural metastatic disease

Objective: To evaluate the profile of patients and tumor features of differentiated thyroid carcinoma (DTC) with biochemical evidence without structurally demonstrable metastatic disease in the postoperative follow-up, regarding the response to empirical radioiodine therapy (RIT). Methods: A retrospective study of 196 patients with DTC followed up at a tertiary service from 1990 to 2018 was performed. All of them presented negative diagnostic whole-body scan (WBS) and high TG levels. Based on criteria indicating greater severity, as higher TG levels, 72 of them received empirical RIT. All remained in follow-up with their outcomes assessed. Results: Carcinoma histopathological characteristics were similar between the groups of patients. In all the assessed moments, TG levels were higher in patients who received RIT than in patients who did not receive it. Regarding WBS after RIT, 57.74% of cases showed uptake, with one-third showing evidence of distant metastasis and 23.94% with cervical uptake in remnant/recurrence of thyroid or lymph node tissue. Patients who received RIT showed a partial reduction in suppressed serum TG, while patients who did not receive RIT exhibited stability of TG during follow-up. Conclusion: After radioiodine therapy administered with biochemical evidence of metastases but without identification of iodine-avid structural disease, metastatic foci avid for iodine were identified in 57% of cases, with a subsequent reduction in serum TG, indicating a potential therapeutic benefit. Despite similar tumor histopathological characteristics, the outcomes differed between patients who received RIT and those who did not, highlighting the importance of individualizing this indication.