KLK3 and prostate cancer: For example, for all six risk factors, the large Zurich cohort, which had the lowest prevalence of high-grade cancer, had the highest or second highest proportion of patients with features associated with reduced prostate cancer risk: PSA ≤ 4 ng/ml, normal DRE, age ≤ 65 years, non-African ancestry, negative family history and a prior negative biopsy.