5074 Background: Although prostate-specific antigen (tPSA) screening reduced prostate cancer (PCa) mortality recent recommendations do not endorse PSA-screening due to overdiagnosis and overtreatment and the resulting harm afflicted to patients. Screening studies showed the maximum benefit in young men < 65 years of age. tPSA and percent free PSA (%fPSA) lack specifity in the diagnosis of PCa. [-2]proPSA and the prostate health index (phi) improved this diagnostic specifity. Markers to diagnose clinicaly relevant cancers in young men are needed. Methods: The clinical performance of [-2]proPSA and phi was evaluated in a multicenter study. A total of 1362 patients scheduled for initial or repeated prostate biopsy (668 with, 694 without PCa, each ≥ 10 core biopsies) were recruited in 4 different sites based on PSA level 1.6 – 8.0 ng/mL WHO-calibrated (2-10 ng/mL classically calibrated). Serum samples taken prior to digital rectal examination (DRE) were measured for the concentration of tPSA, fPSA and [-2]proPSA with Beckman Coulter immunoassays on Access 2 or DxI800 instruments. Phi was calculated as [-2]proPSA/fPSA*√tPSA. Results: In univariate analysis [-2]proPSA/fPSA (%[-2]proPSA) and phi were the best predictors of PCa detection in patients at initial biopsy (AUC: 0,72 and 0,73) and repeated biopsy (AUC: 0,74 and 0,74). Analysis of the data for men ≤ 65 years of age (n=593) showed that %[-2]proPSA and phi significantly improved PCa dectection (AUC: 0,72 and 0,73) as compared with tPSA (AUC: 0,54) or %fPSA (AUC: 0,62). In the detection of significant PCa (based on PRIAS criteria) %[-2]proPSA and phi demonstrated the best performance in the whole cohort and in young men (≤ 65) years as well (AUC 0,68 and 0,73). Conclusions: This multicenter study showed that [-2]proPSA and phi have a superior clinical performance in detecting PCa in the PSA range of 2-10 ng/mL compared with tPSA and %fPSA at initial and repeated biopsies. This superiority is maintained for the detection of PCa in young men (≤ 65 years of age).