KLK1 and prostate cancer: PSA, a serine protein kinase-releasing enzyme specifically secreted by the epithelial cells of prostate,184 is encoded by the prostate-specific gene kallikrein 3 which is a member of the tissue kallikrein family.185 PSA was first identified in the late 1970s.186 The elevated serum PSA levels represent prostate pathologies including prostatitis, benign prostatic hyperplasia, and prostate cancer.187,188 For the early diagnosis of prostate cancer, the positive cut-off value of serum PSA is greater than 10 ng/mL.