a method for activating only the vascular endothelial growth factor receptor - 3 has been created . the method comprises administration of a composition comprising a polypeptide to an animal wherein the composition has the ability to stimulate one or more lymphatic vessel endothelial cells to proliferate , differentiate , migrate , or survive . methods are also provided to selectively activate a vegf receptor - 3 , to screen for neoplastic disease characterized by an increase in lymph vessel endothelial cells , and to identify lymph vessel endothelial cells .