However, a very limited number of validated biomarkers have been utilized in routine practice, such as human epidermal growth factor receptor 2 (HER2/neu) in breast cancer [247], prostate-specific antigen (PSA) in prostate cancer [248], carbohydrate antigen 125 (CA-125) in ovarian cancer [249], and K-Ras mutation in colorectal cancer or non-small-cell lung cancer (NSCLC) [250,251]. Here, KLK3 is linked to colorectal cancer.