Objective: No previous study has reported the numbers of prostate cancer (PC) patients existing among a normal Japanese population with prostate-specific antigen (PSA), > 4 ng/ml. The aim of this study was to elucidate the performance of %free PSA as a screening tool for a normal Japanese population with PSA of 2-4 ng/ml and to examine the characteristics of cancer detected using this criterion. Methods: We conducted a prospective, multi-center study to evaluate the performance of %free PSA among a normal Japanese population. We decided on a %free PSA cutoff value of 12% according to the preliminary results. A total of 5548 consecutive screening volunteers aged 50-79 years were enrolled in the project. Men with total PSA < 4 ng/ml, or men with total PSA of 2-4 ng/ml and %free PSA of ≥ 12% were indicated to undergo 12 core biopsies. Results: There were 826 (14.9%) men with PSA of 2-4 ng/ml. Among them, those with %free PSA of ≥ 12% numbered 100 (12.1%). Forty-nine out of 100 men (49%) received biopsy, and 16 PC patients were detected. Among 10 patients undergoing radical prostatectomy, seven were associated with extra-prostatic extension (pT3) or high-grade cancer (Gleason score 8). Conclusions: We confirmed the ability of %free PSA and demonstrated that there are considerable numbers of PC patients among the normal Japanese population with PSA of 2-4 ng/ml. We ascertained that cancers detected in this study had a variety of tumor characteristics, including those of an aggressive nature.
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