KLK3 and prostate cancer: To further distinguish prostate cancer patients with PSA < 4.0 ng/mL from those with PSA < 4.0 ng/mL, ROC curve analysis was used to obtain three diagnostic models: the sensitivities and specificities were 56.1% and 100% for 5-hydroxymethyl-2-furoic acid, 63.4.0% and 100% for ethylmalonic acid, and 87.8% and 90% for pyroglutamic acid, respectively (Figure 4A).