EVALUATION OF PERCENTAGE OF FREE SERUM PROSTATE-SPECIFIC ANTIGEN TO IMPROVE SPECIFICITY OF PROSTATE-CANCER SCREENING

Objective.-To evaluate measurement of percentage of free prostate-spec ific antigen (PSA) in serum to improve the specificity of prostate can cer screening in men with serum PSA levels between 4.1 and 10.0 ng/mL. Design.-Retrospective, nonrandomized analysis using a research assay for measuring free PSA in frozen serum from men with a spectrum of pro state sizes and digital rectal examination results. Setting.-General c ommunity outpatient prostate cancer screening program at a university center. Patients.-One hundred thirteen men aged 50 years or older, 99% of whom were white, with serum PSA concentrations of 4.1 to 10.0 ng/m L, including 63 men with histologically confirmed benign prostatic hyp erplasia, 30 with prostate cancer with an enlarged gland, and 20 with cancer with a normal-sized gland. All study volunteers had undergone p rostatic ultrasonography and biopsy. Main Outcome Measures.-Percentage of free PSA in serum and percentage of free PSA cutoff that maintaine d at least 90% sensitivity for prostate cancer detection. Results.-Med ian percentage of free PSA was 9.2% in men with cancer and a normal-si zed gland, 15.9% in men with cancer and an enlarged gland, and 18.8% i n men with benign prostatic hyperplasia (P<.001). The percentage of fr ee PSA cutoff was higher in men with an enlarged gland and in those wi th a palpably benign gland. In men with an enlarged, palpably benign g land, a free PSA cutoff of 23.4% or lower detected at least 90% of can cers and would have eliminated 31.3% of negative biopsies. Conclusions .-Measurement of percentage of free serum PSA improves specificity of prostate cancer screening in selected men with elevated total serum PS A levels and can reduce unnecessary prostate biopsies with minimal eff ects on the cancer detection rate; however, further studies are needed to define optimal cutoffs. Final evaluation of PSA screening also mus t consider the ability of current treatments to improve the prognosis of screen-detected prostate cancer.