Measurement of complexed PSA improves specificity for early detection of prostate cancer.
OBJECTIVE
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 addressed the need for improved specificity. Of all these approaches, the free/total PSA ratio appears to be the most promising. Given that most circulating PSA is complexed to alpha1-antichymotrypsin, and that this moiety represents a greater proportion of the total PSA in those men with carcinoma, we set out to determine whether complexed PSA would improve specificity in the detection of men with prostate cancer.


METHODS
Archival sera were obtained from 300 men, 75 of whom had biopsy-proved prostate cancer. All sera had been previously stored at -70 degrees C for variable periods. An investigative assay for complexed PSA (Bayer) was used. The Tandem-R free and total PSA assays (Hybritech) were used according to the manufacturer's recommendations.


RESULTS
Among all patients, specificities for the total PSA, free/total PSA, and complexed PSA alone were 21.8%, 15.6%, and 26.7%, respectively, at cutoffs yielding 95% sensitivity. Similar equivalence or superior performance, in terms of specificity relative to the free/total PSA ratio, was seen at other sensitivity thresholds and other total PSA ranges.


CONCLUSIONS
Complexed PSA alone performs better than total PSA or the free/total PSA ratio and obviates the need for a second analyte determination. We believe this marker may offer significant enhancement in PSA testing with significant economic advantages.
Brawer
M K
MK
Northwest Prostate Institute, Northwest Hospital, and Veterans Administration Health Care System, Seattle, Washington 98133, USA.
Meyer
G E
GE
Letran
J L
JL
Bankson
D D
DD
Morris
D L
DL
Yeung
K K
KK
Allard
W J
WJ
D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000175:diagnosis*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors
D017430:Prostate-Specific Antigen