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    Colon Cancer Patients With Genetic Abnormality Live Longer

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    Microsatellite instability has been found in a high percentage of tumors that occur in people with hereditary nonpolyposis colorectal cancer (HNPCC), an inherited form of colon cancer in which multiple tumors occur at a young age. The genetic abnormality is also found to a smaller degree in "sporadic" colorectal cancers, which arise without any known cause.

    What really has researchers puzzled, however, is why tumors with microsatellite instability appear to be more aggressive -- larger and faster-growing -- than other tumors, but actually have a better prognosis.

    "This is an enigma," says Henry T. Lynch, MD in an interview with WebMD. Lynch, a pioneer of cancer genetics studies, first described HNPCC, also called Lynch syndrome. "Our group did the ... study that confirmed the better prognosis, better survival in each stage. We have no idea why, with the ominous pathology that these patients have, they do better." Lynch is professor of medicine and chairman of the department of preventive medicine at Creighton University School of Medicine in Omaha, Neb.

    He speculates that because the cells are genetically unstable, they may be more susceptible to normal body processes that are designed to remove old or damaged cells. Alternatively, some features of cells with microsatellite instability may make them more vulnerable to the types of drugs used in chemotherapy for colorectal cancer, Lynch says.

    Vital Information:

    • Colon cancer patients under the age of 51 who have a type of genetic abnormality in their tumors called microsatellite instability live longer and are at a lower risk for the disease spreading, according to a new study.
    • Microsatellite instability refers to sections of mismatched DNA that fail to be repaired during cell division.
    • Researchers are puzzled as to why tumors with microsatellite instability signal a better prognosis, even though they are more aggressive than other tumors.
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