[-2]proPSA and the detection of prostate cancer: new data

We are starting to see a increase in the publication of data about [-2]proPSA — a specific type or isoform of free PSA — and its potential relevance in the detection and diagnosis of prostate cancer.

In an article just published, Sokoll et al. report on a relatively large study designed “to characterize the clinical utility of serum [-2]proPSA for prostate cancer detection and assess its association with aggressive disease.”

The study is based on data from 566 eligible patients from a total of 669 subjects enrolled in a prospective prostate cancer detection study at four centers participating in the National Cancer Institute Early Detection Research Network. Serum PSA, free PSA, and [-2]proPSA were measured for all of these patients, using a Beckman Coulter Access 2 Analyzer, and 244/566 (43 percent) of the participants were found to have prostate cancer on biopsy.

Understanding the precise results of this study requires a relatively sophisticated knowledge of statistics. However, the bottom line appears to be the following:

  • The ratio of [-2]proPSA to free PSA, when expressed as a percentage, which is normally referred to as %[-2]proPSA, appears to have “potential clinical utility” for improving the likelihood of prostate cancer detection on biopsy.
  • %[-2]proPSA clearly increased with increasing Gleason score and was higher in patients with more aggressive forms of prostate cancer (i.e., higher Gleason scores).
  • Adding [-2]proPSA data to total PSA data and free PSA data appears to be able to improve the ability to predict the probability of a positive biopsy result — at least in men with a PSA between 2 and 10 ng/ml.

The authors state that, “The addition of %[-2]proPSA could affect the early detection of prostate cancer,” which we take to mean that adding %[-2]proPSA to the standard, serum PSA level, the percentage free PSA level, and perhaps the patient’s age, could help a clinician to determine whether a prostate biopsy is advisable.

Beckman Coulter is planning to commercialize a combination of such PSA data as the Prostate Health Index or phi test. We do not know if Beckman Coulter provided funding to support this study. The still unanswered question, at this time, however, is whether use of %[-2]proPSA data or the Prostate Health Index would actually reduce the need for biopsies in men more likely to have latent or indolent prostate cancer.

The “New” Prostate Cancer InfoLink is definitely in favor of any test that can reliably help physicians and patients to know — before they decide on the need for a biopsy — whether they are at more or less risk for clinically significant prostate cancer. However, it seems a little unclear at this time whether %[-2]proPSA data or the Prostate Health Index will be able to do this reliably in the case of individual patients. We hope that it will be possible to get greater clarity about the value of %[-2]proPSA data in the near future. In an earlier post on this topic, we had already referred to data on 892 patients to be presented at the upcoming AUA annual meeting in San Francisco.

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