Methodological and clinical comparison of the ACS prostate-specific antigen assay and the Tandem-E prostate-specific antigen assay in prostate cancer

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.

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.

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.

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.