PURPOSE: Pro prostate specific antigen (pPSA) is a precursor form of PSA enriched in tumor compared to benign prostate tissues that may be a more specific serum marker for prostate cancer. Serum pPSA was measured in the clinically relevant early detection PSA range of 2 to 10 ng/ml.
MATERIALS AND METHODS: Research use immunoassays were used to measure native and truncated forms of pPSA. The subject cohort contained 1,091 serum specimens from men enrolled in prostate cancer screening studies at 2 sites who had undergone prostate biopsy and were divided into PSA ranges of 2 to 4 ng/ml (benign 320, cancer 235) and 4 to 10 ng/ml (benign 315, cancer 221).
RESULTS: In PSA ranges 2 to 4, 2 to 6, 4 to 10 and 2 to 10 ng/ml, pPSA in a ratio with free PSA (%pPSA) gave the highest cancer specificity. At 2 to 4 ng/ml and 90% sensitivity, %pPSA spared 19% of unnecessary biopsies compared to 10% for free PSA and 11% for complexed PSA(p <0.001). Similar results were obtained at PSA 2 to 6 ng/ml. At 90% sensitivity in the PSA 4 to 10 ng/ml range, %pPSA spared 31% of unnecessary biopsies compared to 20% for % free PSA and 19% for complexed PSA (p <0.0001). In the combined 2 to 10 ng/ml range, %pPSA spared 21% of unnecessary biopsies compared to 13% for % free PSA and 9% for complexed PSA (p <0.0001).
CONCLUSIONS: The %pPSA significantly improved specificity for cancer detection and decreased the number of unnecessary biopsies in the PSA 2 to 4 ng/ml range. This relative improvement of %pPSA compared to % free PSA and complexed PSA was maintained throughout the PSA range of 2 to 10 ng/ml.
INSTITUTION: Washington University, St. Louis, Missouri, USA.
