SERPINE1 and breast cancer: Components of the u-PA system such as u-PA, plasminogen activator inhibitor-1 (PAI-1), and urokinase-type plasminogen activator receptor (u-PAR) are overexpressed in a variety of cancer types, most notably in breast cancer (19), but also in sarcomas (14), and correlate with cancer progression, metastasis and poor prognosis.