Sunitinib-induced autoimmune thyroiditis in a patient with metastatic renal cell carcinoma: a case report.

Sunitinib is an oral multitargeted tyrosine kinase inhibitor that was newly approved by the FDA for the treatment of renal cell carcinoma and imatinib-resistant gastrointestinal stromal tumors. Although generally well tolerated, common side effects of sunitinib have been reported, with an important and well-recognized example being hypothyroidism. Although the exact mechanism of sunitinib-induced hypothyroidism is unclear, some authors have suggested sunitinib might induce hypothyroidism by the blockade of iodine uptake, destructive thyroiditis and inhibition of peroxidase activity. In these studies autoimmune-mediated hypothyroidism could not be demonstrated as an etiological factor. We herein report the case of a 71-year-old woman diagnosed as metastatic renal cell carcinoma with severe autoimmune hypothyroidism associated with sunitinib after 10 months of treatment. To the best of our knowledge, this is the first report that shows sunitinib may induce autoimmune thyroiditis. Further clinical and experimental studies with larger patient groups are required to verify the findings of the present study. Routine monitoring of thyroid autoantibodies including antithyroglobulin and antithyroid peroxidase antibodies and thyroid ultrasonography are recommended during the treatment of sunitinib-induced hypothyroidism.