Although PSA can be affected in many other conditions, such as benign prostatic hyperplasia (BPH), prostatitis, changes in vitamin D, or cardiovascular risk factors, a cut-off value of PSA ≥ 3.0 ng/mL was recommended as an indication for biopsy, and screening of PSA decreased the mortality of prostate cancer in the European Randomised Study of Screening for Prostate Cancer [17,18,19]. Here, KLK3 is linked to prostate cancer.