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    "When many cures are offered for a disease, it means the disease is not curable" -Anton Chekhov

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    Thursday, May 27, 2004

    This Imperfect World: That all too fallible prostate cancer screening test, the PSA, is back in the news. The most recent study says that it's missing too many cancers:

    A study out Thursday confirms that prostate cancer may be present even among patients with so-called "normal" scores on the PSA, or prostate-specific antigen test. Researchers say the findings show that a better screening test is needed.

    ....Doctors who studied nearly 3,000 men found cancers in 15% of those with PSA levels below 4, shows research in Thursday's New England Journal of Medicine. The risk of prostate cancer rose with increasing PSA levels.

    .....Some experts say such findings illustrate the need for more aggressive screening and treatment. The National Comprehensive Cancer Network, a group of 19 leading hospitals, recommended earlier this year that doctors should consider biopsies for men with PSA scores above 2.5.

    But wait, there's more to it. For one thing, most of the cancers were not life threatening:

    When examined under a microscope, however, relatively few of these cancers were found to be dangerous.

    The study's authors noted that the PSA test gives doctors few clues about which cancers will ever threaten a man's life. High scores can be caused by many conditions, from cancer to infections or a benign swelling of the prostate gland that is common in older men.

    ...."There is no magic cutoff below which a man can assume he is completely free of risk or above which he must feel compelled to have a biopsy," said Howard L. Parnes, an author of the study and chief of the prostate and urologic cancer research group at NCI. "We need to get back to basics and allow each man, with the help of his physician, to assess his own risk."

    Exactly. We live in an imperfect world, and unfortunately, prostate cancer is one of the cancers for which we have no good screening test yet. Beware of organizations made up of hospitals and urologists who call for lower thresholds for treatment. They have much to gain from the increased number of biopsies such lower thresholds would produce. Unfortunately, it's far from clear that patients would benefit as well.

    ADDENDUM: Here's the data from the study:

    Among the 2950 men (age range, 62 to 91 years), prostate cancer was diagnosed in 449 (15.2 percent); 67 of these 449 cancers (14.9 percent) [or 2% of the subject population -ed.] had a Gleason score of 7 or higher. The prevalence of prostate cancer was 6.6 percent among men with a PSA level of up to 0.5 ng per milliliter, 10.1 percent among those with values of 0.6 to 1.0 ng per milliliter, 17.0 percent among those with values of 1.1 to 2.0 ng per milliliter, 23.9 percent among those with values of 2.1 to 3.0 ng per milliliter, and 26.9 percent among those with values of 3.1 to 4.0 ng per milliliter. The prevalence of high-grade cancers increased from 12.5 percent of cancers associated with a PSA level of 0.5 ng per milliliter or less to 25.0 percent of cancers associated with a PSA level of 3.1 to 4.0 ng per milliliter.

    And here's what the authors of the study have to say about PSA thresholds:

    A decision to lower the current PSA threshold for biopsy, however, should be considered within the broader context of the PSA-screening debate. Although the use of PSA testing in the United States has led to earlier diagnosis and a marked shift in the stage at which prostate cancer is identified, it is unclear whether PSA testing reduces the rate of death from prostate cancer.....Although clinically important cancers are not always fatal, the large difference between a man's risk of death from prostate cancer (3 to 4 percent) and his lifetime risk of the diagnosis of prostate cancer (16.7 percent) suggests that many prostate cancers detected in routine practice may be clinically unimportant. Lowering the PSA threshold for proceeding to prostate biopsy would increase the risks of overdiagnosing and overtreating clinically unimportant disease.

    posted by Sydney on 5/27/2004 10:06:00 AM 0 comments


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