DUAL MONOCLONAL-ANTIBODY IMMUNOASSAY FOR FREE PROSTATE-SPECIFIC ANTIGEN

Prostate-specific antigen (PSA) is the most important tumor marker for early detection and monitoring of prostate cancer (PCa) patients. PSA is also elevated in many patients with benign prostatic hyperplasia ( BPH). The study of the serum PSA forms, free PSA (f-PSA) and PSA compl exed with alpha(1)-antichymotrypsin (PSA-ACT), may improve the discrim ination between PCa and BPH. An immunoassay specific for f-PSA is repo rted with very low cross-reactivity (0.7%) to PSA-ACT. Serum specimens from BPH and PCa patients (determined by biopsy) with PSA levels from <1 to >100 ng/ml were tested. No f-PSA was detected in serum specimen s from normal females (N=50). Low levels (0-0.3 ng/ml) were detected i n specimens from healthy males (N=60). In specimens from PCa and BPH p atients, the f-PSA to total PSA ratio (fit) was found to range from 1% to higher than 60%. While maintaining an 80% sensitivity for cancer, the fit ratio improved specificity to approximately 80%, as compared t o 55% for total PSA alone. The receiver operating characteristics (ROC ) curve analysis of the fit ratio displayed a greater area under the p lot (0.84) compared to total PSA alone (0.745). The results demonstrat e that the fit ratio significantly increases specificity for PCa detec tion compared to total PSA alone, showing the potential clinical value of the f-PSA immunoassay. (C) 1996 Wiley-Liss, Inc.