Current screening and diagnostic methods, such as colonoscopy for colon cancer, transvaginal ultrasound and the CA125 blood test followed by ovarian biopsy for ovarian cancer, and the prostate-specific antigen blood test and the digital rectal exam followed by prostate biopsy for prostate cancer, are often limited by invasiveness, suboptimal sensitivity and specificity, high costs, and poor patient compliance. Here, KLK3 is linked to prostate cancer.