Prostate specific antigen. Experimental and clinical observations.

A commercially available radioimmunoassay (RIA) for prostate specific antigen (PSA) was investigated in respect to its analytical specificity and its clinical applicability for the diagnosis of prostate cancer. PSA detected in serum by RIA was immunochemically identical to PSA found in seminal plasma. PSA is not a single protein but rather a group of isoproteins with different isoelectric points (pI) in the pH range 6-8. Furthermore PSA could be split in subunits by means of denaturing electrophoresis under reducing conditions. Unlike prostatic acid phosphatase (PAP) serum PSA was stable at room temperature. In sera of patients with benign hyperplasia of the prostate (BPH) two significantly different populations were found. The lower group (0.5-5.8 ng/ml PSA) had PSA values comparable to the control group of apparently healthy males (0.5-6.3 ng/ml). The higher group between 7.7 and 12.2 ng/ml was also characteristic for early stages of prostate cancer (T0 and T1). PSA seemed to be correlated to the tumor volume and allowed to differentiate between early carcinomas of the prostate and BPH or possibly T0/1 staged prostate carcinoma. PSA may be a screening method for early cancer of the prostate.