KLK3 and cancer: Next, enzymes, overexpressed by cancer cells or neovascular tissue in tumors, capable of selective cleavage of prodrugs carrying a peptide substrate moiety, offer several examples: e.g., MMP [34], cathepsin B [35], β-glucuronidase [17,38,39], and PSA [19,41,43] and PSMA [56,60].