Three diagnostic models distinguished prostate cancer patients with PSA < 4.0 ng/mL from those with PSA < 4.0 ng/mL: 5-hydroxymethyl-2-furoic acid (AUC=0.749), ethylmalonic acid (AUC=0.750), and pyroglutamic acid (AUC=0.929). This evidence concerns the gene KLK3 and prostate cancer.