Molecular Forms of Prostate-specific Antigen in Malignant and Benign Prostatic Tissue: Biochemical and Diagnostic Implications

BACKGROUNDPatients with prostate cancer (PCa) show a lower ratio of free prostate-specific antigen (fPSA) to total PSA (tPSA) in serum than patients with benign prostatic hyperplasia (BPH). The patterns of the intracellular PSA isoforms in malignant and benign prostatic tissue have been studied as potential molecular reasons for this phenomenon.METHODSProstatic tissue samples were obtained after cystoprostatectomy from patients with bladder cancer (n = 10), from BPH patients (transurethral resection of the prostate, n = 10; adenomectomy, n = 10), and from the cancerous and noncancerous parts of the same prostates removed surgically by prostatectomy because of PCa (n = 20). PSA pattern was characterized by gel filtration, immunoblotting, and immunoassays for tPSA, fPSA, alpha(1)-antichymotrypsin-PSA (ACT-PSA), and complexed PSA (Bayer Immuno 1 assay). Comparisons were made with the PSA concentrations in serum.RESULTSThe major portion of tPSA in all tissue samples was fPSA; complexed PSA forms were <2%. Samples from cystoprostatectomy patients had the lowest and those from adenomectomy patients the highest values of tPSA and fPSA. PSA concentrations were lower in cancerous than in the noncancerous parts of the prostate. No significant correlations were found between tumor stage or grade and the amounts of tPSA, fPSA, and ACT-PSA in tissue. Tissue PSA values were not correlated with the serum PSA concentrations nor with the ratios fPSA/tPSA and ACT-PSA/tPSA in sera.CONCLUSIONSThe amounts of tPSA and the PSA isoforms in prostatic tissue explain neither the concentrations of tPSA and PSA isoforms in serum nor the behavior of the ratio fPSA/tPSA in patients with BPH and PCa.