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Blood test may detect colon cancer risk
WASHINGTON (Reuters) -- A simple blood test may be able to predict who is at risk of colon cancer -- offering a way to avoid the embarrassing ordeal of a colonoscopy, U.S. researchers said on Thursday. They found a single genetic change that was much more common in people with a family history of colon cancer -- and extremely common in people diagnosed with colon cancer. The researchers said more studies must be done to ensure results are consistent, but they hope they have found a simple and accurate way to screen a healthy population for colon cancer. "There are screening tests for cancers with rare family syndromes," Dr. Andrew Feinberg of Johns Hopkins University in Baltimore, who led the study team, said in a telephone interview. An example is the breast cancer gene BRCA1, which causes perhaps 5 percent of all inherited breast cancers. "And there are tests to screen for the presence of cancer, like the PSA test, for example," he added -- referring to the prostate specific antigen test that can show prostate cancer. "But there are no tests for just screening the population to identify people who have a genetic risk of cancer." Colorectal cancer is the second leading cause of cancer death in the United States after lung cancer. The American Cancer Society predicts 147,000 people will be diagnosed with colorectal cancer this year and 57,000 will die of it. Health officials advise everyone over the age of 50 to get a colonoscopy to check for colon cancer or the little growths that can become cancerous. These growths can be removed at the time of the examination, perhaps preventing cancer completely. But people are reluctant to get the tests, and patients with a genetic risk can develop the disease much earlier. The Centers for Disease Control and Prevention said on Thursday that only 53 percent of U.S. men and women aged 50 years and older had any type of colorectal cancer screening. Looking for genetic mistakesFeinberg, Hengmi Cui, Marcia Cruz-Correa and others tested 172 patients at a colonoscopy clinic. They were looking for a specific genetic change called loss of imprinting. This is not a genetic mutation, but a mistake in how the genes work. People get two copies of each gene -- one from each parent -- but some are imprinted so that only one copy works. Feinberg's lab had previously found that a gene called IGF2, which controls production of insulin-like growth factor 2, had "loss of imprinting" in some forms of cancer. "In this case both copies are working. This is a gene for cell growth and it makes sense that getting a double dose might lead to cancer," he said. They looked for this change both in the blood and in samples taken from the patients' colons. Those who had colon cancer or who had it in the past were nearly 22 times as likely to have the change, they found -- and they could detect it in the blood in most cases. Now they will have to see if other patients who had the change go on to develop cancer, Feinberg said. And if the tests hold true in larger groups of people, it may be possible to develop a quick blood test to look for colon cancer risk, Feinberg said. There is no proven way to prevent colon cancer other than to remove the polyps, but people without the genetic change may be able to skip colonoscopies, or have them less often. There are also studies that suggest taking aspirin or related drugs such as ibuprofen or COX-2 inhibitors daily can prevent colon cancer, although this has not been proven. Copyright 2003 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
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