Background: At present, empirical radioactive iodine therapy is recommended for patients with thyroid cancer and elevated thyroglobulin (Tg) after initial therapy when neck ultrasonography (US), chest computed tomography (CT), and 18-fluorodeoxyglucose positron emission tomography (FDG-PET) do not reveal metastases. The objective of this study was to determine whether empirical (131)I therapy is indeed useful in these patients.
Methods: Patients with papillary thyroid cancer submitted to total thyroidectomy followed by remnant ablation with (131)I in whom whole-body scanning at the time of ablation (WBS-ablation) did not reveal metastases and who had elevated Tg after initial therapy were selected. Included in the study were patients with basal Tg >2 ng/mL or Tg >5 ng/mL after stimulation with recombinant human thyrotropin or Tg >10 ng/mL after levothyroxine withdrawal for 4 weeks. All patients were first investigated by neck US and chest CT. FDG-PET/CT was performed in patients with negative US and CT. The final sample of this study consisted of patients with negative US, CT, and FDG-PET/CT. These patients received an activity of 100 mCi (131)I and were submitted to posttherapy WBS (RxWBS).
Results: Among the 24 patients receiving empirical (131)I therapy, no ectopic uptake was seen in 23 and mild uptake in the thyroid bed (<0.5%) in 15. Only one patient presented pulmonary metastases detected by RxWBS. Disease was observed in two other patients during short-term follow-up (mean 22 months), one with lymph node metastases diagnosed by a repeat US and one with bone metastases diagnosed by CT and FDG-PET scans.
Conclusions: We conclude that RxWBS rarely reveals disease in patients with elevated Tg after ablation, but with negative findings on WBS-ablation, US, CT, and FDG-PET. In this situation, empirical (131)I therapy should be restricted to patients with documented progression of serum Tg.