Assays for detecting and determining the presence of prostate cancer is
provided. The assays are capable of detecting prostate cancer in the
population of men with a significantly higher ratio of free PSA to total
PSA. The assays are also capable of detecting prostate cancer in the
population of men with a low amount of total PSA, i.e., in the range of 2
to 4 ng/ml. In accordance with one embodiment of the present invention,
the assay includes the steps of (a) determining the amount of total PSA
contained in a biological sample from the patient, (b) determining the
amount of free PSA in the sample; and calculating the ratio of the free
PSA to the total PSA, (c) determining the amount of pPSA in the sample,
(d) determining the amount of BPSA in the sample, (e) determining the
amount of inPSA in the sample, and (f) correlating the amount of inPSA
contained in the sample to the presence of prostate cancer in the patient
by comparing the amount of inPSA to a predetermined value established
with control samples of known cancer and benign disease diagnosis, based
on both the level of total PSA and the % free PSA.