INFLUENCE OF FREE-TO-TOTAL PROSTATE-SPECIFIC ANTIGEN VARIABILITY ON THE EARLY DIAGNOSIS OF PROSTATE-CANCER - A COMPARATIVE-STUDY OF 3 IMMUNOASSAYS

Objective To compare three immunoassays for total prostate specific an tigen (tPSA), free PSA (tPSA), free-to-total PSA ratio (f/tPSA), and t he f/tPSA thresholds for optimal differentiation between benign prosta tic hypertrophy (BPH) and prostate cancer in 141 consecutive patients referred for prostatic disease. Patients and methods The study include d 43 patients with prostate cancer and 98 with BPH, all confirmed hist ologically. PSA levels were assessed using the following assay Ir;its just before histological analysis of the prostate; Hybritech (Tandem-R PSA, normal values, NV, <4 ng/mL, and Tandem-R free PSA), Cis Bio (PS A-RIACT, NV <2.5 ng/mL and fPSA-RIACT) and Immunocorp (PSA-IRMA, NV <4 ng/mL, and Free PSA-IRMA). The results were assessed to determine the sensitivity, specificity and threshold values of the different assays to differentiate patients with BPH and cancer. Results The mean tPSA and f/tPSA ratio were statistically different in assays with different NVs. The mean fPSA values differed significantly between the Hybritec h and Cis Bio, between the Hybritech and Immunocorp but not between th e Cis Bio and Immunocorp assays. With receiver operator curve analysis , there were no statistically significant differences among the three immunoassays in f/tPSA (0.72 for Hybritech, 0.73 for Cis Bio and 0.64 for Immunocorp) or between the tPSA and fPSA curves for each manufactu rer. With the sensitivity fixed at 90%, different f/tPSA thresholds we re defined (0.22, 0.34 and 0.25 for Hybritech, Cis Bio and Immunocorp, respectively). The specificities (i.e. the percentage of unnecessary biopsies spared) were 22%, 21% and 31%, respectively (not significantl y different). Conclusion Each immunoassay could be used to distinguish prostate cancer and BPH at different f/tPSA thresholds, with 21-30% o f unnecessary biopsies spared. There was no difference in overall perf ormance among the different assays. Further studies are needed to bett er define the exact use of the f/tPSA ratio in the routine diagnosis o f prostate cancer.