Findings from a trial of 18,882 healthy men 55 years of age or older reported that only 20% of men with PSA ≥ 4.0 ng/mL actually had the disease, and 6% of men who do not have prostate cancer falsely tested positive at this threshold (Ankerst and Thompson, 2006). Here, KLK3 is linked to Familial prostate cancer.