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Detecting Signs of Colon Cancer in Blood
  
By Adam Marcus

More men get screened regularly for prostate cancer than for colon tumors, despite the fact that colon cancer is a deadlier disease. One reason for this may be that there’s a blood test for prostate cancer while colon cancer requires an unpleasant exam in the doctor’s office.

Now, however, scientists have developed a blood test that may one day help doctors predict who's at high risk for colorectal cancer. Though still in the experimental stages, the test detects a chemical “imprint” that silences one copy of a particular gene. When the imprint is lost, the normally silent gene can become active and lead to tumors.

The loss of the imprint is associated with an increased risk for the disease, and its value as a predictor of the disease is not yet known. But researchers can now use the imprint as a “biomarker” to track individuals over time and see if they develop colon cancer.

"You have to see what happens to these people after the test is done before you would want to apply it to patients," says Andrew Feinberg, a cancer geneticist at the Johns Hopkins University School of Medicine, in Baltimore, Maryland, and a co-author of the study. The study, reported in Science, found that people with colon cancer were 21 times more likely to lose the imprint than those without the disease.

In previous research, Feinberg and his colleagues found that about 30 percent of people with colon cancer or a family history of the disease are missing the imprint. As a result, they make too much of a protein called insulin-like growth factor (IGF2), which spurs colon cells to proliferate out of control.

In the latest study, Feinberg's group found that the protein could be detected in blood.

The chances of losing the imprint were five times higher for people with a family history of colon cancer than in others.

The researchers are trying to determine if the lost imprint plays a role in both hereditary and spontaneous colon cancers. As many as half of colon cancer cases are thought to be linked to heritable factors, while the rest likely occur spontaneously.

The experimental test is specific to the loss of imprinting and doesn't detect other disease-related changes, notes David Ransohoff, a cancer expert at the University of North Carolina, Chapel Hill, and author of a commentary accompanying the journal article.

“But one could imagine that you could make a group of tests and this would be among them,” he says.

Earlier this month, the Seattle biotech firm Epigenomics announced a three-year, $100 million deal with Swiss drug giant Roche to develop screening tests for cancers using ‘epigenetic’ signals like those at work in certain colon cancers.

“The products being developed as part of this collaboration address the urgent need for earlier detection of cancer in bodily fluids by more accurate screening tests,” said Heino von Prondzynski, head of Roche Diagnostics, in a statement about the deal.

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Cui, H. et al. Loss of IGF2 imprinting: A potential marker of colorectal cancer risk. Science 299, 1753-1755 (March 14, 2003).
 

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