Serine proteases, e.g. plasmin, thrombin, urokinase (uPA), and the KLKs (kallikrein-related serine peptidases) regulate diverse biological processes such as general protein turnover, embryogenesis and pregnancy, blood coagulation, complement activation, and wound healing.1 More specifically, serine proteases are involved in cell proliferation and cell signaling, cell migration and invasion, apoptosis and cell death, not only under physiological conditions but also in cancer. This evidence concerns the gene KLK4 and cancer.