uPAR (Urokinase plasminogen activator receptor) is a 55 kDa glycoprotein I-anchored surface receptor specific for urokinase plasminogen activator (uPA). Upon binding to uPAR, uPA converts the surface bound, large serum β-globulin, plasminogen to plasmin. Plasmin, which is also designated fibrinolysin, is a trypsin-like enzyme that acts on Arg-Lys bonds and induces pericellular proteolysis in fibrin and fibrinogen, and thereby contributes to the systematic activation of the coagulation cascade. uPA and uPAR are known to be overexpressed in mesenchymal and epithelial tumor cells and are required for tumor invasion and metastasis.