PSA Precursor May Detect Prostate Cancer Better

A study has found that an inactive precursor of prostate-specific antigen (PSA) may prove better than standard PSA testing for detecting prostate cancer and identifying more aggressive forms. The findings were presented at the annual meeting of the American Association for Cancer Research in Washington (DC, USA).

PSA tests measure "free” and "bound” PSA but often fail to distinguish between slow-growing cancers and more-aggressive cancers, which are likely to grow quickly and spread. PSA consists of several molecular forms including proPSA, which is a precursor form of the enzyme shown to be a more cancer-specific marker of prostate cancer.

Researchers retrospectively analyzed 1,091 blood serum samples from men enrolled in prostate cancer screening studies who had undergone prostate biopsy (PSA 2-4 ng/ml: 320 benign, 235 cancer; PSA 4-10 ng/ml: 315 benign, 221 cancer). Throughout the 2-10 ng/ml range, levels of proPSA were measured using research immunoassays to determine the efficacy for detecting cancer. Analysis showed that proPSA was a better marker than the other forms of PSA (total, free, and complex) at detecting cancer throughout the 2-10 ng/ml range. ProPSA superiority was strongest in the 2-4 ng/ml range. In addition, it more accurately identified aggressive forms of cancer by Gleason Score discrimination in the 2-4 and 4-10 ng/ml range. Commercially available assays for free, total, and complex PSA were not effective in predicting cancer below 4 ng/ml. Since as many as 25% of men with PSA values below 4 ng/ml may have prostate cancer, the biopsy cutoff mark of 4 ng/ml is controversial.

"These results may significantly alter the current standard for screening of prostate cancer by enabling detection at a cutoff below 4 nanograms and reducing the number of unnecessary biopsies,” said co-investigator Stephen Mikolajczyk, staff research scientist at Beckman Coulter, Inc. (Fullerton, CA, USA).




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