Complexed prostate specific antigen (PSA) reduces unnecessary prostate biopsies in the 2.6-4.0 ng/mL range of total PSA.

OBJECTIVE

To compare the performance of complexed prostate-specific antigen (cPSA) to total PSA (tPSA) and percentage free PSA (f/tPSA) in the diagnosis of prostate cancer for the tPSA range 2.6-4.0 ng/mL.

PATIENTS AND METHODS

Consecutive men scheduled for prostate biopsy were enrolled prospectively at 14 different sites in two multicentre studies in Europe and the USA. Serum obtained before biopsy was tested with the ACS:180 and Immuno 1 tPSA and cPSA assays (Bayer Diagnostics, Tarrytown, NY, USA) and the Access fPSA and tPSA assays (Beckman, Inc., San Diego, CA, USA). Receiver operating characteristics (ROC) curves were generated to compare the diagnostic performance of tPSA, cPSA and f/tPSA.

RESULTS

Of 316 men with a tPSA of 2.6-4.0 ng/mL, 82 (26%) were diagnosed with prostate cancer on biopsy. ROC analysis of all 316 men showed an area under the curve (AUC) for cPSA of 0.63, significantly greater than the AUC for tPSA of 0.56 (P = 0.008). At a sensitivity of 95%, threshold values of 2.3 ng/mL for cPSA and 2.73 ng/mL for tPSA provided specificities of 20.1% and 9.8%, respectively. f/tPSA was only available for 205 of the 316 (65%) men and the AUC for cPSA was 0.63, and did not significantly differ from the f/tPSA AUC of 0.64 (P = 0.58).

CONCLUSIONS

As a single test, cPSA provides improved specificity over tPSA and comparable specificity to f/tPSA for detecting prostate cancer, and may reduce the number of unnecessary prostate biopsies in the 2.6-4.0 ng/mL tPSA range.