VSP inhibitor-induced hypothyroidism is seen as a consequence of inhibition of the ret proto-oncogene product, suppression of iodine uptake and peroxidase activity, and induction of capillary regression.64 Regression of capillaries has been observed in a number of organs (especially endocrine organs) in adult rodents treated with VSP inhibitors.66 In the study by Chu et al.,8 five out of 36 patients (14%) on sunitinib developed hypothyroidism at a mean time of 54 weeks. This evidence concerns the gene RET and hypothyroidism.