New DNA Test Catches Colon Cancer

Genetic marker may help identify malignancies without need for colonoscopy

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HealthDay Reporter

FRIDAY, April 16, 2004 (HealthDayNews) -- A new test that identifies DNA changes in your stool could lead to a noninvasive way of screening for colon cancer, a study finds.

An Austrian research team found that by testing stool samples for changes in DNA methylation, which is a form of genetic alteration common in colorectal cancer cells, they were able to identify colorectal cancer about 90 percent of the time.

"There are certain type of changes in DNA that are specific to certain tumors," said lead researcher Dr. Martin Widschwendter, a professor of obstetrics and gynecology from the Medical University of Innsbruck. One of these is called DNA methylation, he explained.

According to Widschwendter, earlier fecal DNA tests for colorectal cancer have looked at gene mutations. However, these tests are not nearly as accurate as this new one.

Widschwendter's team looked for the most promising DNA methylation markers from a long list of candidate genes by looking for DNA changes in stools of cancer patients and healthy controls.

To confirm their finding, they then tested for these potential markers in stool samples from 49 subjects -- two sets of patients and healthy controls, according to their report in the April 17 issue of The Lancet.

They found that a gene known as SFRP2 was methylated more frequently in DNA from the stools of patients with colorectal cancer than in it was in stool samples from people without cancer.

Although other DNA mutation markers have been identified in stool that predict colorectal cancer, the SFRP2 gene is the most accurate predictor of colorectal cancer found so far, Widschwendter said.

"What we are aiming for is to combine all these methylation markers with gene mutation markers to develop a simple test that will be 100 percent accurate," he said. Patients who have a positive test would then go on to have a colonoscopy, Widschwendter added.

The same researchers are also publishing a report that says they can identify endometrial cancer (a cancer of the lining of the uterus) from DNA changes in vaginal specimens, Widschwendter said.

Widschwendter believes this method can also be used to identify cervical cancer and other cancers by sampling blood and other body fluids and looking for specific DNA changes.

"This approach will open up a new and exciting way to screen for cancers," he said.

"This is a very encouraging study," said Dr. Douglas K. Rex, a professor of medicine from the Indiana University School of Medicine and president of the American College of Gastroenterology.

The currently available DNA markers are not a good as a colonoscopy in identifying cancer, so adding another marker could be a big advance, he said.

Using this marker along with other markers may be an effective way of diagnosing colorectal cancer, Rex said.

However, he cautioned that until a large screening test is done to see how well this test detects cancers in a large population, it remains only an interesting preliminary finding.

Dr. Durado Brooks, director of colorectal cancer at the American Cancer Society, commented that the study is interesting and is a new way of looking at fecal DNA analysis.

One problem Brooks noted is the researchers excluded patients with adenomas, which are precancerous polyps.

"One of the benefits of screening is that you can find these adenomas before they turn into cancer and remove them. If you have a screening method that is good for finding cancer but doesn't find adenomas, then you are not providing a benefit to patients," Brooks said.

If they could identify patients with precancerous polyps, that would increase the likelihood that this test could have some clinical significance, he added.

"It's a good start," Brooks said. "Hopefully, it will lead to more intensive work. But it won't alter clinical practice in the near future."

Researchers are constantly looking for better ways to identify colorectal cancer early, when it is highly treatable. Experts were disappointed earlier this week by a study finding that virtual colonoscopy, a highly touted, less invasive screening method for the disease, failed to find 61 percent of small polyps. By comparison, a standard colonoscopy detected 99 percent of those polyps.

More information

The National Cancer Institute can tell you about colorectal cancer and the Colon Cancer Alliance can tell you more about screening for the disease.

SOURCES: Martin Widschwendter, M.D., professor, Department of Obstetrics and Gynecology, Medical University Innsbruck, Austria; Douglas K. Rex, M.D., professor of medicine, Indiana University School of Medicine, Indianapolis and president, American College of Gastroenterology; Durado Brooks, M.D. director, colorectal cancer, American Cancer Society, New York; April 17, 2004, The Lancet

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