The subgroup analysis of PSA levels divided into groups of ≥ 4.0 ng/mL and < 4.0 ng/mL showed that patients with 1-PSA ≥ 4.0 ng/mL (groups a, d, and e) and those with 1-PSA < 4.0 ng/mL but with 2-PSA ≥ 4.0 ng/mL (group b) had a significantly higher incidence of prostate cancer than those with 1-PSA and 2-PSA of < 4.0 ng/mL (group f) (Supplementary Table S4). This evidence concerns the gene KLK3 and prostate cancer.