KLK4 and benign prostatic hyperplasia: As KLK4 is overproduced by premalignant prostate epithelial cells as well as PCa cells and PAR1 is deregulated in the reactive stroma associated with BPH and PCa (Ramsay et al., 2008b; Wang et al., 2010; Zhang et al., 2009), we hypothesize that KLK4–PAR1 interactions play an important role in prostate stromal cell activation.