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Researchers Find Genetic Flaw Responsible For Colon Cancer

By Rick Weiss
The Washington Post


Researchers Thursday an-nounced they have identified the genetic flaw that causes as many as one in six cases of colon cancer, as well as a number of other fatal cancers of the uterus, ovaries and other organs. The faulty gene, believed to be present in more than 1 million Americans, may be the single biggest cause of inherited cancer.

Scientists said the discovery is the most significant advance yet toward understanding the molecular underpinnings of hereditary cancers. It also offers the first opportunity to apply DNA tests to large numbers of people with family histories of cancer to determine with a high degree of certainty whether they will get the disease.

"It's a stunning achievement," said Francis S. Collins, director of the National Center for Human Genome Research in Bethesda, Md., which helped fund the research. "This is the advance that's going to push us into the era of genetic medicine. It's no longer in the future. Genetic studies are going to be an everyday part of medical practice."

Researchers involved in the work said a relatively simple blood test to detect the defective gene could be available within six months, although its use would be limited at first to people with a family history of colon cancer.

The newly identified gene causes hereditary non-polyposis colon cancer, a form that typically strikes by age 50 and has been known to occur in children as young as 8.

The gene's discovery marks the climax of a hotly contested race that had two competing laboratories working night and day for the past six months.

One team, led by Richard Kolodner of the Dana Farber Cancer Institute in Boston and Richard Fishel of the University of Vermont report their discovery in Friday's issue of the journal Cell. Results from the second team, led by Bert Vogelstein and Kenneth W. Kinzler at The Johns Hopkins Oncology Center will appear in that journal's Dec. 17 issue. The teams announced their findings at a joint news conference Thursday at the National Institutes of Health.

"This would be considered by many to be one of the most important medical discoveries of the decade," said Henry T. Lynch, president of the Hereditary Cancer Institute at Creighton University School of Medicine in Omaha and a pioneer in the field. "As far as hereditary-cancer syndromes are concerned, this is probably the most common one of them all, so this discovery is absolutely exciting and mind boggling."

Researchers emphasized that most of the 152,000 cases of colon cancer that arise in the United States each year are not inherited but are caused by the accumulation of spontaneous genetic mutations throughout life. The latest discovery is not likely to have an immediate impact on these cases.

But it may have a profound effect on the approximately one in 200 Americans who unknowingly harbor the newly discovered defective gene, most of whom have watched helplesslesly as family members fell ill.

Until now, individuals in these colon cancer-prone families have had no way to know whether they had inherited the deadly gene. Members of such families typically submit to an annual colonoscopy -- an expensive procedure that allows a physician to view the upper reaches of the large intestine to look for tumors in their earliest stages. When these tumors are caught early, survival rates can reach 90 percent.

But if an accurate blood test for the responsible gene is developed, family members will be able to know with near certainty whether they've inherited the defective gene. Those without it can relax. "The anxiety associated with this disease is immense," said Vogelstein.

But even a positive test has benefits, he said. Those who definitely have the problem gene are more likely to get regular colonoscopies. Moreover, a positive test can provide incentive to make healthful changes in lifestyle. Studies suggest a high-fiber, low-fat diet can reduce the risk of colon cancer. Daily doses of aspirin may also help.

"What you're seeing here is a long-awaited shift toward early detection and prevention in colorectal cancer," said Nicholas Petrelli, chief of surgical oncology at Roswell Park Cancer Institute in Buffalo, N.Y. "We're going to be able to select out the people who are going to get this disease, and intervene early. This is a tremendous advancement."

The usefulness of the new finding is not limited to colon cancer. Women harboring the altered gene have a 50- to 70-percent chance of developing uterine cancer and a 10- to 15-percent chance of ovarian cancer, which is difficult to detect early. Other cancers, including an unknown portion of non-inherited colon cancers, have also been linked to the newly detected defect.

With a little more research, scientists said, it should be possible to develop a blood test that is sufficiently accurate and cost-effective to be offered to the population at large.

Collins and others warned, however, that technical and ethical hurdles will have to be overcome before such a test is made available. Issues of privacy are foremost, since insurance companies and employers may be inclined to reject those with genetic predispositions to cancer.