New DNA Detector for Colon Cancer

      - A new non-invasive DNA test of stool samples can accurately screen for colon cancer and may be only three years away from general use, Mayo Clinic scientists reported today.

      The technique was found to be more than 90 percent effective in detecting colon cancer and might soon replace other current screening options, such as testing stool samples for blood, according to researchers and the Massachusetts genomics company who developed the test.

      "This test safely and accurately detected curable-stage cancer of the colon and rectum," says lead author Dr. David Ahlquist, a gastroenterologist at the Mayo Clinic in Rochester, Minn., and lead author of the study, which was published in the journal Gastroenterology . "The new DNA test has the potential to save thousands of lives."

      Cancer Killer

      Colon cancer is the second leading cause of cancer deaths in this country, with 130,000 men and women diagnosed with the disease annually. Over 56,000 Americans will die of the disease each year. Warning symptoms can include blood in the stool and intestinal problems, but they are not always apparent.

      Doctors say if the slow-progressing disease is caught early enough using screening methods, there is a 95 percent survival rate. But a recent survey by the American Gastroenterology Association in Bethesda, Md., found that fewer than half of all Americans were undergoing the recommended (yet often, unpleasant) tests.

      The American Cancer Society currently advises those at average risk get screened for colon cancer starting at age 50 and those at high-risk, such as those with a family history, begin sooner.

      The group''s recommendations include an annual test for blood in the stools, called a fecal occult blood test, which can indicate cancer, as well as a flexible sigmoidoscopy every five years, or a barium enema and subsequent x-ray of the colon every five to ten years, or a colonoscopy every ten years.

      A sigmoidoscopy uses a tube to inspect the lower colon in a doctor''s office, while a colonoscopy requires bowel preparation and hospitalization, done on an outpatient basis, but checks the entire colon. Patients found to have abnormal stool samples will then be given the full colonoscopy, which can remove any cancers or pre-cancerous polyps instantly.

      Colonoscopes contain small cutting devices which can be theaded through the tube to remove growths.

      New Screening Technique

      The new DNA-based test is similar to the fecal occult blood test in that patients or doctors simply take a swab of a stool sample for diagnosis, without having to undergo the more invasive tests.

      But the blood test only has a 50 percent chance of catching advanced cancers in a single screening and will miss the majority of earlier polyps. The test only detects whether blood is oozing from an advanced cancerous cell, but the presence of blood could also be a result of other non-cancerous conditions, such as a benign polyp or an abnormal blood vessel.

      The new DNA test instead collects cells shed from the lining of the colon and amplifies the genetic material, looking for indications of mutations at those earlier stages of cancer.

      "This is potentially a huge advantage," Ahlquist says. "Testing for DNA makes more biological sense than blood; it reflects the pathology that''s there."

      Genetic Mutants

      The DNA test currently looks at seven specific genes previously identified by researchers as being identified with colon cancer. As new cancer-linked genes are identified, they could be added to the test, Ahlquist says.

      When these genes, such as the P53 and the k-RAS genes are mutated, they can cause a loss in a piece of a chromosome or cause cells to lose their ability to correct errors in the genetic sequence, resulting in abnormal cell growth. Doctors can use colonoscopy to remove problematic growths in patients found to have the mutations.

      In this pilot study, researchers tested 61 patients-22 who had colon cancer, 11 who had pre-cancerous polyps and 28 percent who had healthy colons. The DNA test picked up 91 percent of the patients with cancer and 73 percent of the patients with polyps. Those without colon cancer were also diagnosed correctly as healthy. The researchers were not aware of the patients'' status when they performed the test.

      Because the technique looks only at specific cancer-causing gene mutations, the test is more targeted than the test for blood in the stool, allowing for the greater accuracy and lack of false positives (or incorrectly diagnosing a healthy colon as cancerous) according to EXACT Laboratories Inc., the 5-year-old Maynard, Mass.-based company who developed the proprietary technology for the test.

      Study Set to Begin

      Ahlquist and other researchers at the Mayo Clinic will be leading a 3-year, $4.9 million clinical trial funded by the National Cancer Institute set to begin in January to test the method. They will use the technique on 3,000 patients at average risk for colorectal cancer at six different medical centers nationwide.

      Ahlquist says if the results are "knock-your-socks-off," they hope to apply for Food and Drug Administration approval of the method immediately and make the test available at the doctor''s office soon afterwards.

      The cost of genetic screening, not yet determined by company, is likely to be higher than the fecal occult blood test, which is currently $10 to $20 dollars. But because the test had no "false positives," Ahlquist hopes it could eliminate the need for patients to suffer expensive but unnecessary colonoscopies which can cost up to $1,500 a piece.

      That may make any higher up-front cost cheaper in the long run, he says, reducing the overall $7.5 billion spent annually to diagnose and treat the disease.

      This, as well as other new screening techniques in development, such as "virtual" colonscopy using x-rays and video capsules a patient can swallow, are going to change screening in the next five years, says Dr. David Fleischer, a past president of the American Society for Gastrointestinal Endoscopy and a professor of medicine at Georgetown University Medical Center.

      Patients Shouldn''t Procrastinate

      But Dr. Sidney Winawer, a gastroenterologist at the Memorial Sloan-Kettering Cancer Center in New York City, reminds patients that although this technique sounds "promising," currently available screening tools are also effective.

      "This is a very early stage research paper-it''s not anything that can re

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