von Willebrand Factor (vWF) is a multimeric glycoprotein that is found in endothelial cells, plasma and platelets. It acts as a carrier protein for Factor VIII and promotes platelet adhesion and aggregation. vWF undergoes a variety of posttranslational modifications that influence the affinity and availability for Factor VIII, including cleavage of the propeptide and formation of N-terminal disulfide bonds. This antibody helps to establish the endothelial nature of some lesions of disputed histogenesis, e.g. Kaposi s sarcoma and cardiac myxoma. It is widely used for differentiating vascular lesions from those of other tissue differentiation within a panel of other vascular markers although not all tumors of endothelial differentiation contain this antigen.