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    Aspirin Blocks Only Some Colon Cancer

    Study IDs People Who Benefit Most From Aspirin Use; Could Lead to New Treatments
    WebMD Health News
    Reviewed by Louise Chang, MD

    May 23, 2007 - New insights into how colorectal cancers develop could lead to a targeted approach for using aspirin and other anti-inflammatory drugs to prevent the disease.

    While regular aspirin use has been shown to lower colorectal cancer risk, the risks associated with frequent use are believed to outweigh the benefits. Serious side effects of regular aspirin use include ulcers and bleeding of the stomach.

    But a new study, led by researchers from Harvard Medical School and Massachusetts General Hospital, raises hopes of identifying and treating only those who would benefit most from aspirin therapy.

    The widely held belief that aspirin lowers colorectal cancer risk by reducing inflammation led the researchers to examine the expression of the Cox-2 enzyme in colorectal tumors.

    “Cox-2 is an enzyme that is associated with inflammation, and it has become clear that some cancers express this enzyme and others do not,” researcher Andrew T. Chan, MD, MPH, tells WebMD.

    36% Risk Reduction

    Chan and colleagues hypothesized that frequent aspirin use would protect against colorectal cancers that expressed Cox-2, but not those that didn’t.

    They tested the theory by examining the medical records of 130,000 participants in two large, ongoing health trials. They also examined the lab reports of 600 tumor specimens from people in the studies who developed colorectal cancer.

    Their findings appear in the May 24 issue of TheNew England Journal of Medicine.

    Overall, Chan and colleagues found that people who took at least two standard aspirin tablets a week had a lower risk of developing colorectal cancer than nonaspirin users.

    But their analysis of cancer samples revealed that the risk reduction was seen only in tumors expressing the Cox-2 enzyme.

    Roughly two-thirds of the tested tumors had moderate or strong Cox-2 expression, while the remaining third did not.

    Chan tells WebMD that regular aspirin use was associated with a 36% reduction in the risk of developing Cox-2-positive tumors. Aspirin use did not appear to influence the risk of developing Cox-2-negative tumors.

    Precancerous Polyps

    Aspirin and other Cox-2 inhibiting therapies, like the drug Celebrex, are known to help prevent the colorectal polyps that can lead to cancer.

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