Summary: Type I plasminogen activator inhibitor (PAI-1) is a 50 kDa serpin family member that inhibits tissue- and urokinase-type plasminogen activators (tPA, uPA). This protein appears to be an important regulator of plasminogen activation by tPA and extracellular proteolysis by uPA. The plasminogen activator proteolytic enzyme systems are important not only for fibrinolysis but also for extracellular matrix remodeling and have been implicated in a number of normal and pathological processes including angiogenesis, ovulation and embryogenesis, thrombotic and hemorrhagic disorders, connective tissue diseases, neoplasm, and sepsis. PAI-1 is a prognosticator in breast cancer, gastric cancer, various forms of lung cancer, and cervical cancer.