Although PSA is highly specific for the prostate, it is not prostate cancer–specific, since PSA serum in the blood may be increased in many situations, such as prostate cancer, urinary retention, benign prostatic hyperplasia, DRE, ejaculation, perineal trauma, prostate biopsy, prostate surgery, and prostatitis, and may be decreased by approximately 50% in patients taking 5-alpha reductase inhibitors such as finasteride and dutasteride (National Comprehensive Cancer Network [NCCN], 2016). This evidence concerns the gene KLK3 and male reproductive organ cancer.