SERUM PROSTATE-SPECIFIC ANTIGEN COMPLEXED TO ALPHA-1-ANTICHYMOTRYPSIN AS AN INDICATOR OF PROSTATE-CANCER

Prostate specific antigen (PSA) in serum has recently been shown to occur in complex with alpha1-antichymotrypsin and as an approximately 30 kDa. noncomplexed molecular form. We characterized PSA by 3 different assays in samples from 144 patients with benign prostatic hyperplasia (BPH) and 121 with carcinoma of the prostate. One of these noncompetitive assays measured total PSA by detecting PSA complexed to serine proteinase inhibitors and the noncomplexed molecular form, a second measured only PSA in complex with alpha1-antichymotrypsin, whereas a third detected the noncomplexed form. PSA in complex with alpha1-antichymotrypsin was the predominant form in all patient sera. Noncomplexed PSA constituted a minor fraction that was significantly smaller in patients with untreated prostate cancer than in those with BPH (p <0.0001). The proportion of noncomplexed PSA does not correlate to the serum concentration of PSA or that of alpha1-antichymotrypsin. In men with a serum PSA concentration of less than 10 mug./l. the combination of assays measuring total PSA immunoreactivity, the noncomplexed molecular, form and PSA in complex with alpha1-antichymotrypsin may facilitate discrimination between prostate cancer and BPH.