Significance of Thyroglobulin Autoantibodies in Patients With Thyroid Cancer Treated With Lenvatinib

Context Serum thyroglobulin (Tg) is a highly sensitive and specific tumor marker, employed in post-operative management of patients with differentiated thyroid carcinomas. Tumor shrinkage of radioiodine-refractory thyroid cancer (RAIR-DTC) treated with multitarget kinase inhibitors as lenvatinib, expressed according to the Response Evaluation Criteria in Solid Tumors (RECIST), is also associated with a drastic reduction of Tg levels. However, interference caused by circulating thyroglobulin autoantibodies (TgAb) represents the main limitation in the clinical use of Tg. Objective To evaluate if in RAIR-DTC TgAb could be considered a surrogate marker of Tg in monitoring response to treatment with lenvatinib. Design We retrospectively evaluated patients who had started lenvatinib and correlated serum Tg and TgAb with the radiological response across visits. Setting University of Pisa, Italy. Patients We selected 9/97 RAIR-DTC patients with detectable TgAb. Intervention None. Main Outcome Measure(s) None. Results Tg values correlated neither with TgAb title nor with radiological response across visits. Greater decreases in TgAb titer correlated with favorable radiological response to lenvatinib after 1 month (Spearman's correlation = 0.74, P = .021) and 6 months (correlation = 0.61, P = .079). According to RECIST, patients with partial response showed a ∼10-fold greater decrease in TgAb compared to those with stable disease at 1 month (median TgAb decrease: −142 vs −14 IU/mL, P = .01) and those with progressive disease at 6 months (median TgAb decrease: −264 vs−24 IU/mL, P = .04). Conclusion TgAb evaluation may represent a reliable surrogate marker for Tg trend in evaluating response of RAIR-DTC to treatment with lenvatinib. A multicentric study would be useful to confirm our results.