Genetic risk factor found for colon cancer
July 8, 2007
Research teams from Canada, Britain and the United States have identified a genetic variation on chromosome 8 that is linked
to colon cancer, a finding that could lead to a way to better identify who needs more regular screening for the disease.
The three projects all found the same marker in populations from Ontario, Newfoundland and Labrador, Scotland, France,
Seattle and Britain, as well as in five ethnic subpopulations of the United States Americans of African, Japanese,
Hawaiian, Latino and European heritage.
The consistency of the results was described as “virtually incontrovertible proof” that this genetic change on chromosome 8
is associated with a modest but real increase in the risk of colon cancer as well as prostate cancer and perhaps more forms
of the disease.
“At least to our knowledge this is the first common genetic risk factor that has been reproducibly associated with risk of
multiple cancers,” said Christopher Haiman, from the Keck School of Medicine at the University of Southern California and
lead author of the American paper.
All three papers were published online today by the journal Nature Genetics.
“Now the association observed with this variant in prostate and colorectal cancer provides very strong support for the
hypothesis that there may be a common biological mechanism underlying cancer risk in this region of the genome.”
The work 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,” said Dr. Tom Hudson, president of the Ontario Institute of Cancer Research.
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 Canada project. It’s 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 who did not, 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.”
The variant, in a region of chromosome 8 called rs6983267, is associated with other types of cancers as well. That suggests
unlocking its secrets may help scientists better predict who among those who have it are at increased risk of developing
these cancers and who might not be.
Dr. Terry Sullivan, president and CEO of Cancer Care Ontario, explained the finding should eventually help medicine screen
people who have some but not an extensive family history of colon cancer. People whose families are rife with colon cancer
cases already know they are at vastly elevated risk of developing the disease.
But that is not true for people with this genetic variant. They have some increased risk the different research teams put
it at roughly 20 per cent. But that is an average. For some people with this marker, the risk would be greater; for others,
it would be less.
“This initiative will help us in a way be more precise about what kind of surveillance is required for people with familial
risk factors,” said Sullivan, who is not an author of any of the papers.
It is estimated that people with some family history of colon cancer make up about 20 per cent of all colorectal cancer
cases.
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.”
SOURCE : Canadian Press