Background. The objective of this study was to evaluate the clinical significance of measuring the free-to-total (f/t) prostate-specific antigen (PSA) ratio for the differentiation of prostate cancer from benign prostatic hypertrophy (BPH) and for the staging of prostate cancer in Japanese men. Methods. Before treatment, tPSA and fPSA were measured in 147 patients with prostate cancer and in 253 with BPH, using immunofluorometric techniques. Furthermore, the f/t PSA ratio and the tPSA density of the whole prostate (PSAD) were calculated. Results. The tPSA and PSAD levels in patients with prostate cancer paralleled the clinical stage, and were significantly higher than the levels in patients with BPH, while the f/t PSA ratio was not associated with clinical stage, despite the significantly lower values in prostate cancer patients than in BPH patients. Furthermore, the tPSA and PSAD values, but not the f/t PSA ratio, were significantly different between patients with pathologically extraprostatic disease and those with organ-confined disease. Calculation of the specificity of each assay within the range of 80%-95% sensitivity showed that tPSA and PSAD provided better specificities than the f/ t PSA ratio. However, there was no significant difference in specificities among these three assays. In prostate cancer and BPH patients with PSA values of 4.1-10 ng/ml, the specificities of tPSA and PSAD were also superior to that of the f/t PSA ratio. Conclusion. These findings suggest that measurement of the f/t PSA ratio does not provide any significant additional information for the diagnosis and staging of prostate cancer in Japanese men when tPSA and PSAD values are available.
