SUCCESS OF MOLECULAR STAGING OF PROSTATE CANCER
Some scientists have been impressed by initial reports of this test’s success:
In one recent study, researchers obtained blood from radical prostatectomy patients before they underwent surgery. They compared the frequency of a positive PCR test for PSA (which means cells in the blood were able to secrete PSA) to a man’s pathologic stage of cancer. In this study, 87 percent of the men with positive surgical margins, and 83 percent of men with positive seminal vesicles, had a positive PCR test.
Pretty strong results! However, we must not over-interpret them. Here’s why: For years, it has been known that cancer cells can be present in the blood of patients with many different types of cancer that can still be cured. (The cancer is curable because these cells have not yet developed the ability to survive at distant sites.) In fact, in the study mentioned above, 25 percent of patients with curable cancer had a positive PCR test; their test results were “false positives.” And this tells us something we already knew, that just because a man has cancer cells circulating in his blood, this doesn’t mean his cancer can’t still be cured.
For this reason, we believe that a man’s treatment decisions should not be based on this test until more is known about it. Finally, another matter for scientists to explore is the possibility that this PCR test may not even be a true measure of PSA. It may actually be measuring a molecule that bears a striking resemblance to PSA but isn’t PSA.
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