Purpose: We studied whether adding percent free PSA to total PSA improves prediction of clinically significant prostate cancer and fatal prostate cancer.
Materials and methods: A total of 6,727 men within the intervention arm of PLCO (Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial) had baseline percent free PSA. Of this cohort, 475 had clinically significant prostate cancer and 98 had fatal prostate cancer. Cumulative incidence and Cox analyses were conducted to evaluate the association between percent free PSA/PSA and clinically significant prostate cancer/fatal prostate cancer. Harrell's 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 percent free PSA was 18%. Cumulative incidence of fatal prostate cancer for men with baseline PSA ≥2 ng/mL and percent free PSA ≤10 was 3.2% and 6.1% at 15 and 25 years, respectively, compared to 0.03% and 1.1% for men with percent free PSA >25%. In younger men (55-64 years) with baseline PSA 2-10 ng/mL, C index improved from 0.56 to 0.60 for clinically significant prostate cancer and from 0.53 to 0.64 for fatal prostate cancer with addition of percent free PSA. In older men (65-74 years), C index improved for clinically significant prostate cancer from 0.60 to 0.66, with no improvement in fatal prostate cancer. Adjusting for age, digital rectal exam, family history of prostate cancer, and total PSA, percent free PSA was associated with clinically significant prostate cancer (HR 1.05, P < .001) per 1% decrease. Percent free PSA improved prediction of clinically significant prostate cancer and fatal prostate cancer for all race groups.
Conclusions: In a large U.S. screening trial, the addition of percent free PSA to total PSA in men with baseline PSA ≥2 ng/mL improved prediction of clinically significant prostate cancer and fatal prostate cancer. Free PSA should be used to risk-stratify screening and decrease unnecessary prostate biopsies.
Keywords: biomarkers; prostate-specific antigen; prostatic neoplasms.