Free PSA improves prediction of prostate cancer

Adding percent free prostate-specific antigen (PSA) to total PSA results in better prediction of clinically significant prostate cancer and fatal prostate cancer in men, reports a study.

A team of investigators performed Cox analyses to explore the relationship between percent free PSA/PSA and clinically significant prostate cancer/fatal prostate cancer. They used Harrell’s C index to assess predictive ability and conducted Kaplan-Meier analysis to evaluate survival.

The study included 6,727 men within the intervention arm of PLCO* Screening Trial with baseline percent free PSA, of whom 475 had clinically significant prostate cancer and 98 fatal prostate cancer. Median follow-up was 19.7 years. Participants had a median baseline PSA of 1.19 ng/mL, while the median percent free PSA was 18 percent.

In men with baseline PSA ≥2 ng/mL and percent free PSA ≤10 percent, the cumulative incidence of fatal prostate cancer was 3.2 percent at 15 years and 6.1 percent at 25 years relative to 0.3 percent and 1.1 percent, respectively, in men with percent free PSA >25 percent.

In younger men (aged 55‒64 years) with baseline PSA 2‒10 ng/mL, C index for clinically significant prostate cancer improved to 0.60 from 0.56 and for fatal prostate cancer to 0.64 from 0.53 with the addition of percent free PSA. In older men (aged 65‒74 years), C index for clinically significant prostate cancer improved from 0.60 to 0.66, with no improvement seen for fatal prostate cancer.

Percent free PSA correlated with clinically significant prostate cancer (hazard ratio, 1.05; p<0.001) for every 1-percent decrease after adjusting for age, digital rectal exam, family history of prostate cancer, and total PSA.

Notably, percent free PSA led to improvements in predicting clinically significant prostate cancer and fatal prostate cancer for all race groups.

“Free PSA should be used to risk-stratify screening and decrease unnecessary prostate biopsies,” the investigators said.

*Prostate, Lung, Colorectal, and Ovarian Cancer