[Sunitinib and hypothyroidism]

Sunitinib inhibits numerous tyrosine kinase receptors involved in tumor growth, angiogenesis, and metastatic invasion. It is indicated in case of metastatic renal carcinomas and gastrointestinal stromal tumors (GIST) resistant to imatinib. Prospective and retrospective studies have shown association between use of sunitinib and hypothyroidism affecting more than 50% of patients in some series. More amazing, was the non-visualisation of thyroid tissue evaluated with thyroid ultrasonography in two cases. Mechanisms of this side effect are not elucidated. Some studies have suggested destructive thyroiditis but no evidence of autoimmunity has been demonstrated. Anti angiogenic effect could be another hypothesis. Recently antithyroperoxidase activity of sunitinib has been demonstrated. Because hypothyroidism is easily accessible to treatment, screening of thyroid abnormalities is mandatory every three months to improve quality of life of these patients. This unique thyroid side effect of sunitinib with the non-visualisation of thyroid suggests a possible and promising antitumor activity in thyroid cancer.