The role of serum thyroglobulin (Tg) in this scenario is not entirely clear: Whereas short-term rises of serum tumor markers (calcitonin, carcinoembryonic antigen [CEA]) not reflecting tumor progression have been reported in patients with medullary thyroid carcinoma (MTC) during TKI treatment15, the corresponding kinetics of Tg in radioiodine-refractory DTC patients have not been investigated yet. Here, CEACAM5 is linked to medullary thyroid gland carcinoma.