Certain cells secrete uPA and express uPAR at low levels [52] however, hormones [53,54,55,56], growth factors [55,57,58,59], cytokines [60,61] and tumour promoters [62,63,64], which also affect cellular proliferation and differentiation, induce overexpression of these components [65] in a variety of cancer cell lines. Here, PLAU is linked to cancer.