KLK3 and colorectal cancer: In recent years, some tumor-specific proteins have been identified as biomarkers for various cancers to assist and guide final diagnosis; for example, cancer antigen 125 (CA125) for ovarian cancer [31], carbohydrate antigen 19-9 [32,33] for pancreatic cancer, α-fetoprotein (AFP) [34,35] for hepatocellular cancer, carcinoembryonic antigen (CEA) [36] for colorectal cancer, and prostate-specific antigen (PSA) [37] for prostate cancer.