MEASUREMENT OF COMPLEXED PSA IMPROVES SPECIFICITY FOR EARLY DETECTIONOF PROSTATE-CANCER

Objectives. Prostate-specific antigen (PSA) is the most useful of all tumor markers. Although the sensitivity is impressive, low specificity results in a lack of cancer detection in a significant proportion of patients undergoing prostate biopsy. Several recent studies have addre ssed the need for improved specificity. Of all these approaches, the f ree/total PSA ratio appears to be the most promising. Given that most circulating PSA is complexed to alpha(1)-antichymotrypsin, and that th is moiety represents a greater proportion of the total PSA in those me n with carcinoma, we set out to determine whether complexed PSA would improve specificity in the detection of men with prostate cancer. Meth ods. Archival sera were obtained from 300 men, 75 of whom had biopsy-p roved prostate cancer. All sera had been previously stored at -70 degr ees C for variable periods. An investigative assay for complexed PSA ( Bayer) was used. The Tandem-R free and total PSA assays (Hybritech) we re used according to the manufacturer's recommendations. Results. Amon g all patients, specificities for the total PSA, free/total PSA, and c omplexed PSA alone were 21.8%, 15.6%, and 26.7%, respectively, at cuto ffs yielding 95% sensitivity. Similar equivalence or superior performa nce, in terms of specificity relative to the free/total PSA ratio, was seen at other sensitivity thresholds and other total PSA ranges. Conc lusions. Complexed PSA alone performs better than total PSA or the fre e/total PSA ratio and obviates the need for a second analyte determina tion. We believe this marker may offer significant enhancement in PSA testing with significant economic advantages. UROLOGY 52: 372-378, 199 8. (C) 1998, Elsevier Science Inc. All rights reserved.