• Division of Urology, Brigham and Women's Hospital, Boston, Massachusetts.
• Channing Division of Network Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
• Departments of Surgery (Urology Service) and Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York.
• Department of Pathology and Laboratory Medicine, Surgery, and Medicine at Memorial Sloan Kettering Cancer, New York, New York.
• Department of Epidemiology, Harvard T.H Chan School of Public Health, Boston, Massachusetts.
• Department of Urology, University of Chicago, Chicago, Illinois.

INTRODUCTION: We studied whether adding percent free prostate-specific antigen (%fPSA) to total PSA improves prediction of clinically significant prostate cancer (csPCa) and fatal PCa.

METHODS: 6727 men within the intervention arm of the Prostate, Lung, Colorectal and Ovarian Trial had baseline %fPSA. Of this cohort, 475 had csPCa and 98 had fatal PCa. Cumulative incidence and Cox analyses were conducted to evaluate the association between %fPSA/PSA and csPCa/fatal PCa. Harrell's concordance-index (C-index) evaluated predictive ability. Kaplan-Meier analysis assessed survival.

RESULTS: Median follow-up was 19.7 years, median baseline PSA was 1.19 ng/mL, median %fPSA was 18%. Cumulative incidence of fatal PCa for men with baseline PSA≥2 ng/mL and %fPSA ≤10 was 3.2% and 6.1% at 15 and 25 years, compared to 0.03% and 1.1% for men with %fPSA >25%. In younger men (55-64 yr) with baseline PSA 2-10 ng/mL, C-index improved from 0.56 to 0.60 for csPCa and from 0.53 to 0.64 for fatal PCa with addition of %fPSA. In older men (65-74 yr), C-index improved for csPCa from 0.60 to 0.66, while no improvement in fatal PCa. Adjusting for age, digital rectal exam, family history of PCa, and total PSA, %fPSA was associated with csPCa (HR 1.05, P < .001) per 1% decrease. %fPSA improved prediction of csPCa and fatal PCA for all race groups.

CONCLUSION: In a large US screening trial, the addition of %fPSA to total PSA in men with baseline PSA ≥2 ng/mL improved prediction of csPCa and fatal PCa. Free PSA should be used to risk-stratify screening and decrease unnecessary prostate biopsies.