Prostasomes — another possible marker for prostate cancer aggression?

A story in Science Daily, based on new article in the Proceedings of the National Academy of Sciences (PNAS) , has suggested that blood levels of “prostasomes” may be a more accurate marker for prostate cancer risk that PSA levels in blood. So what is a “prostasome”?

Some 30 years ago a young Swedish researcher called Gunnar Ronquist was able to demonstrate that prostate cells make large amounts of a very small membrane-coated particle that is commonly found in semen. He named these particles “prostasomes.” (Note: It is important to distinguish carefully between “prostasomes” and the molecules known as “proteasomes,” which have a very different type of function.)

It is still not entirely clear to the current writer exactly what the normal role of prostasomes is in male fertility and sexual transmission of genetic information. However, according to the paper by Tavoosida et al. in PNAS, in men with prostate cancer, rather than accumulating in semen, prostasomes are (for some reason) “pumped out into the surrounding cancer tissue.” As a consequence, prostasomes can be expected to occur at elevated levels in the serum samples of these patients.

Tavoosida et al. have (so far) been able to do three things.

In the first place they have been able to develop a test that can identify prostasomes in serum (a test that did not exist until recently). They have then been able to apply this test to show that levels of prostasomes in serum levels of prostate cancer patients seem to correlate more closely with the severity of the disease than do PSA levels.

Specifically, the authors have shown that the average (median) levels of prostasomes in blood plasma of patients with prostate cancer were 2.5 to 7.0 times higher than the protasome levels in the plasma of control samples (in two independent studies). Furthermore, they have also been able to use the prostasome levels to distinguish between patients with post-prostatectomy Gleason scores  of 7 and 8/9 and patients with Gleason score ≤ 6. In other words, they seem to have found a blood-based test that may be able to act as a proxy for the aggressiveness of prostate cancer.

The potential value of a blood- or urine-based test that could distinguish with accuracy between men with post-surgical Gleason scores of ≤ 6, 7, and ≥ 8 is potentially considerable. However, it would be unwise to think (based on the limited data available to date) that this prostasome test is “the answer.” A great deal more work will be needed before anyone could suggest with confidence that prostasome levels in serum offered an accurate proxy for Gleason scores in a patient before he was even given a biopsy.

One Response

  1. It’s a start … which is more than the recent suggestion that the current PSA test should be dropped. Time to start clinical trials.

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