Methodological and clinical comparison of the ACS prostate-specific antigen assay and the Tandem-E prostate-specific antigen assay in prostate cancer.
OBJECTIVES: The new ACS prostate-specific antigen (PSA) assay was methodologically and clinically compared with the established Tandem-E PSA assay. We intended to find a possible advantage in primary diagnosis and monitoring the recurrence of prostate cancer due to the additional better recognition of the free PSA form by the ACS PSA assay. METHODS: sera of 51 healthy men, 127 patients with hyperplasia, and 82 untreated patients with prostate cancer were analyzed by means of the Tandem-E PSA assay (Hybritech) and the ACS PSA assay (Ciba Corning). Follow-up was done on 12 cancer patients with recurrences. RESULTS: Both assays correlated very well (r = .98 for all studied men or hyperplasia patients or cancer patients). However, both assays did not yield comparable values: The ACS assay was characterized by nearly doubled values compared with the Tandem-E assay. At 95% specificity versus patients with benign hyperplasia, cutoff values were obtained as follows: 28.8 ng/mL for the ACS PSA assay and 15.2 ng/mL for the Tandem-E assay. At 95% specificity versus hyperplasia patients, we calculated sensitivities of 60% (ACS PSA) and 63% (Tandem-E PSA). Our longitudinal study revealed more prominent slopes for the ACS assay in patients with recurrent cancer disease. However, using either the ACS assay or the Tandem-E assay, the PSA increase started at the same time. In 1 patient, the increasing ACS PSA accelerated 3 months earlier than the increasing Tandem-E PSA did. CONCLUSIONS: The ACS assay has obviously higher PSA levels. The clinician is not familiar with such high PSA levels. The specificity-sensitivity profile nonetheless remains unchanged. If the PSA concentration is measured by the ACS assay, patients who relapse will reveal a more rapid PSA increase. Then, recurrent cancer disease may be detected earlier in some cases.