Predictive factors of radioiodine ablation success: results from a MEDIRAD prospective clinical study for thyroid cancer.

Objective: Serum thyroglobulin measurements are used in the long-term management of patients with differentiated thyroid cancer following thyroidectomy and radioiodine therapy. The use of predictive biomarkers, such as post-operative stimulated thyroglobulin levels and absorbed dose, may help to identify patients at risk of disease recurrence or an unsuccessful initial treatment. Methods: Differentiated thyroid cancer patients treated with 1.1 or 3.7 GBq of radioiodine using recombinant human thyrotropin stimulation or thyroid hormone withdrawal were recruited into observational clinical studies in France, Germany and the UK with aligned study endpoints (MEDIRAD). The maximum absorbed dose to the thyroid remnant was determined and compared to post-operative stimulated thyroglobulin with respect to its ability to predict ablation success. Radioiodine therapy success was defined as unstimulated or stimulated thyroglobulin level of <0.2 or <1.0 ng/mL 9-12 months post-radioiodine. Results: Ninety-four patients had follow-up data and negative antithyroglobulin antibody tests. Seventy-eight patients (83%) were deemed excellent biochemical responders. Post-operative thyroglobulin and maximum absorbed dose predicted ablation success with receiver operating characteristic area under the curves of 0.83 ± 0.05 (P < 0.001) and 0.64 ± 0.08 (P = 0.12). A dose-response relationship between maximum absorbed dose and ablation success was found for patients with a post-operative stimulated thyroglobulin of ≥1 ng/mL. Conclusions: Predictions of ablation success using post-operative stimulated thyroglobulin or the absorbed dose to the thyroid remnant could inform personalisation of management of differentiated thyroid cancer and identify patients where further treatments or more intensive follow-up are required. Patients with a post-operative stimulated Tg of <1 ng/mL likely do not benefit from radioiodine.