Abstract
Hypothyroidism is a frequently occurring complication in patients on lenvatinib treatment. However, little is known about lenvatinib-induced thyrotoxicosis and destructive thyroiditis. We herein report the cases of three patients who developed hyperthyroidism during the course of lenvatinib treatment. All patients had multiple hepatocellular carcinoma of Child-Pugh class A. Two patients required beta blockers for the management of palpitations. One patient developed hyperthyroidism only one week after the initiation of lenvatinib treatment. Thus, the possibility of hyperthyroidism developing within one week after the first administration should be kept in mind, and periodic surveillance of the thyroid function should be performed during the early period of lenvatinib therapy (within the first two weeks or so after the initial administration).