Lenvatinib , an oral inhibitor of vascular endothelial growth factor receptors 1 , 2 , and 3 , fibroblast growth factor receptors 1 through 4 , platelet-derived growth factor receptor , RET , and KIT , showed clinical activity in a phase 2 study involving patients with differentiated thyroid cancer that was refractory to radioiodine ( iodine-131 ) .