Marker in the blood may be used to test for colon cancer risk
Thursday, March 13th 2003, 12:00 am
By: News On 6
WASHINGTON (AP) _ Researchers have found a biological marker that may lead to a simple blood test to screen for colon cancer, possibly replacing some invasive techniques now used to check for the killer disease.
A subtle molecular change that switches on a usually inactive gene has been linked by researchers at Johns Hopkins University to an increased risk of developing colon cancer.
The molecular change can be detected in a blood test and could one day be used routinely to predict a patient's chances of developing colon cancer, said Dr. Andrew P. Feinberg, senior author of the study appearing Friday in the journal Science.
``Up to now, there have been no tests for common cancer risks,'' said Feinberg. ``There are for other diseases, but not for cancer. Ultimately, that's what we hope this test will do.''
Colon cancer is the third most deadly cancer in America. Each year about 148,000 new cases are diagnosed and about 56,000 people die from the disease. It is considered one of the most curable of the serious cancers because its early stages can be detected with a colonoscopy. But studies have shown that many patients dread and avoid the test, which involves drinking several quarts of a solution to clean the colon, followed by being probed with a medical instrument.
A blood test that accurately defines a patient's colon cancer risk could reduce the need for such invasive procedures, experts say.
In the Hopkins study, Feinberg and his team analyzed blood samples from 172 patients who had had colonoscopies. The researchers were searching for chemical evidence of a process called ``loss of imprinting,'' or LOI, in the insulin-like growth factor, or IGF2, gene.
Two copies of this gene are inherited, one from each parent, but normally only the copy inherited from the father makes the growth factor. The IGF2 gene copy from the mother is silenced by the attachment of a molecule made up of carbon and hydrogen, a process called methylation.
In the loss of imprinting, methylation fails and the maternal IGF2 gene is turned on, giving the patient ``a double whammy'' of growth factor, said Feinberg.
Based on the analysis of the 172 patients, the Hopkins team found that those with a family history of colon cancer were five times more likely to have the LOI marker. Patients who had polyps, an early stage of cancer development, were three times more likely to have LOI, while patients with a personal history of colon cancer were 22 times more likely to have LOI. Among healthy patients with no family history of cancer, about one in 10 had the LOI marker.
Feinberg said that to prove LOI is a valid marker for colon cancer, the researchers will have to look at blood samples from many more randomly selected patients and follow them for several years. He said it may be five years before the test would be ready for general use.
``If the test proves out, then it could be used in the same way that lipid (cholesterol) testing is done now to evaluate heart disease risk,'' said Feinberg. He said people found to be at higher risk of colon cancer could then have further testing and close follow-up, while those with no indication of risk would need less monitoring.
Dr. Paul J. Limburg, director of the colorectal cancer center at the Mayo Clinic, said the Feinberg study ``has the potential to be an important advance'' in the detection of colon cancers.
``It would be very desirable to have a simple way to test patients through their blood to predict their risk of cancer in the colon and in organs as well,'' said Limburg. ``Markers like this one may allow us to do that.''
The study was funded by the National Cancer Institute, and the technology being developed is licensed by Hopkins to a firm called Epigenomics AG. Feinberg and some members of his team are entitled to a share of any royalties developed from the technology.