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Two Genes Cause Colon Cancer

By Thomas H. Maugh II
Los Angeles Times

With the discovery of a second colon cancer gene, researchers reported Wednesday that they now have identified the causes of more than 90 percent of the inherited form of the disease.

Together, the two genes are responsible for one in every six of the 156,000 new cases of colon cancer diagnosed each year. They also appear to account for as many as 30 percent of sporadic (noninherited) cases of colon cancer.

Researchers expect within a few months to develop diagnostic tests that will show whether an individual has either gene. If one of the genes is present, doctors can monitor for tumors frequently, enabling their detection while they are still curable by surgery.

"We can reduce cancer deaths in these families by over 90 percent," said Dr. Bert Vogelstein of Johns Hopkins University, a co-leader of one of the two groups that report the discovery Thursday in the British journal Nature and Friday in Science.

The discovery could also lead to new anticancer drugs within three to five years, predicted microbiologist Richard Fishel of the Unversity of Vermont, a leader of the team that reported its findings in Nature. "I am very confident that in short order we will be able to develop appropriate therapeutics based on our knowledge of these genes," he said.

The same two teams reported the discovery of the first colon cancer gene in December.

Both genes, which are found on different chromosomes, act like the spell-check function in a word processing program, checking newly synthesized DNA to ensure that no mistakes -- mutations -- occur during cellular proliferation. When either gene is defective, "You accumulate these alterations at an extremely high rate and cancer is the result," said Fishel. Inherited colon cancer usually strikes before the age of 50.

"This is a great triumph for science," said Department of Health and Human Services Secretary Donna E. Shalala. "These discoveries ... will lead to screening tests for high-risk individuals soon. Doctors will be able to save countless lives and prevent much needless suffering."

But Shalala raised the concern, shared by the researchers, that screening for the impaired gene could hinder the ability of people who have the gene to purchase health insurance. Because virtually everyone who has the gene will develop cancer, carriers might be excluded from coverage. About one in every 200 people has one of the defective genes, Vigelstein said, making it the most common genetic defect in the world.