Genetic variation linked to colon cancer

Scientists from around the world have found a new genetic marker for colon cancer, which they hope will help better identify those people who are at higher risk of the disease.

The researchersanalyzed the genes of thousands of people, including those fromCanada, England and theU.S., to look for common markers that signalled colon cancer. The results from the three research projects were published online Sunday by the journal Nature Genetics.

The consistency of the results was described as "virtually incontrovertible proof" that the genetic change on chromosome 8 is associated with a modest but real increase in the risk of colon cancer and other cancers.

"We also know that it's a risk factor for prostate and breast, so it's not specific to colon cancer," said Dr. Tom Hudson, presidentof Toronto's Ontario Institute for Cancer Research, who led the Canadian research team. "It increases risk to cancer in general."

About 30 to 40 per cent of the population carries the genetic marker, but not all of them will get cancer, he said.

Hesaid he hopesthe finding will one day lead to a simple blood test that will identify people who have it, so that they can be monitored more closely.

"If we can start identifying who is at higher risk for colon cancer, for example, you would start doing early screening in those individuals at an earlier age," he said.

But some doctors who treat patients wonder just how valuable this will turn out to be. Having the marker raisesone's risk of getting colon cancer fromeight per cent to nine or 10 per cent.

The small difference is not big enough for there to be a change in the way patients are screened, said Dr. Malcolm Moore of Princess Margaret Hospital in Toronto.

Results of groundbreaking project

The research is one of the early fruits of the groundbreaking HapMap project, the atlas of DNA differences between people that scientists believe will help them zero in on the genetic causes of diseases.

"Before, when you were finding genes, you were lucky. Today, we have [the equivalent of] sonar to look deeply at every region of the genome,"Hudson said.

Hudson is a senior author of one of the papers, which was the product of the ARCTIC,or Assessment of Risk for Colorectal Tumours in Canadaproject a collaboration of researchers from Canada, the United States, France, Scotland and England.

The Canadian-led study looked at genetic coding for 7,480 people with colorectal cancer and 7,779 people without it, drawing subjects from Ontario, Newfoundland, Seattle, Scotland and France. In total, the three papers looked at about 17,550 people with the disease and 19,500 without.

"The reason we all hit this gene is we all had access to a new technology last year," Hudson said, referring to the three research papers.

"Variations on the approach, but we all got to the same point because this is a true gene."

Colorectal cancer is the fourth most common form of cancer in Canada, and the second most deadly, after lung cancer. The Canadian Cancer Society estimates that 20,800 Canadians will be diagnosed with colon cancer this year and 8,700 Canadians will die of the disease.

But when caught in the early states, colon cancer is a highly treatable form of the disease. And a simple and accurate screening test, if one could be made, would go a long way toward cutting back on those unnecessary deaths, Hudson said.

"If I identify who's at risk I can bring them in. I can look for blood in the stool or I can bring them in for a colonoscopy and look. And if there's a small tumour we take it out and there's a 100 per cent cure rate," he said.

"It's going to save lives. If you pick up small tumours and take them out, people live longer."