Clinical usefulness of percentage of free serum prostate specific antigen.

Serum concentrations of total and free prostate specific antigen were measured retrospectively in 268 patients, in order to test the usefulness of percentage of free prostate specific antigen in distinguishing between cancer and benign hyperplasia of the prostate and to improve the specificity of cancer screening. Four groups were investigated: 94 urologic patients without prostate disease (controls), 98 patients with a histologically confirmed benign hyperplasia, 76 with histologically established prostatic adenocarcinoma, 18 of them after radical prostatectomy. Total and free prostate specific antigen concentrations were measured in frozen serum, in a retrospective mode, by using an equimolar monoclonal antibody immunoassay. Median percentage of free prostate specific antigen was 20.48% in controls, 17.75% in patients with hyperplasia, 10.52% in patients with cancer and 33.03% in patients after prostatectomy. Median percentage of free prostate specific antigen was significantly lower in men with cancer than in patients with benign hyperplasia (P < 0.0001). The percentage of free prostate specific antigen increased the specificity of cancer screening: a cut-off of 23.6% detected at least 90% of cancers and would have eliminated 34.7% of biopsies in benign hyperplasias. A prospective study is ongoing to confirm these results.