KLK3 and prostate cancer: On the other hand, although PSA is still used as a golden-standard biomarker to screen prostate cancer and its metastasis, our results found that the expression of PSA was unable to discriminate bone metastatic prostate cancer cases from non-bone metastatic prostate cancer cases after the number of bone metastatic prostate cancer cases was increased from 16 cases in Cohort I to 41 cases in Cohort II (Figure 2A-B).