Despite the fact that most patients with DTC had received large doses of radioiodine and some had received external beam radiation therapy, both of which have myelosuppressive potential, treatment with sunitinib was well tolerated in most patients with DTC as well as in the patients with MTC. These results are encouraging, but, as our series was small and did not evaluate efficacy, more extensive studies in DTC and MTC are needed to determine the possible roles of sunitinib in these very different tumors.