VWF (von Willebrand Factor) is a multimeric plasma glycoprotein involved in hemostasis and platelet aggregation and adhesion to the subendothelial matrix. It is found in endothelial cells, megakaryocytes, and found within the subendothelial connective tissue matrix, in intravascular plasma as well as in areas of hemorrhage. Inherited VWF deficiency is associated with bleeding disorders such as von Willebrand Disease. The protein is useful for the identification of tumor angiogenesis, vascular tumors, and metastatic osteosarcomas. References: Blood Transf 2011 9(Sup2):s3; Crit Rev Clin Lab Sci 2007 44(2):115.