Elevated expression levels of urokinase and several other components of the plasminogen activation system are found to be correlated with tumor malignancy. It is believed that the tissue degradation following plasminogen activation facilitates tissue invasion and, thus, contributes to metastasis. Urokinase-type plasminogen activator (uPA) is more commonly associated with cancer progression than tissue plasminogen activator (tPA). This makes uPA an attractive drug target, and, so, inhibitors have been sought to be used as anticancer agents. However, incompatibilities between the human and murine systems hamper clinical evaluation of these agents. Moreover, urokinase is used by normal cells for tissue remodeling and vessel growth, which necessitates distinguishing cancer-associated urokinase features for specific targeting.