Researchers find new, more accurate way to detect precancerous and curable-stage colorectal cancer

October 23, 2000

DNA Test Could Significantly Change Current Screening Methods

ROCHESTER, MINN. -- Mayo Clinic researchers working in collaboration with scientists at EXACT Laboratories, Inc. of Maynard, Mass have developed a new, non-invasive test that was 91 percent sensitive for detecting cancer throughout the colon, according to a study released today in the journal Gastroenterology. Each year, 56,000 people in the United States die from cancer of the colon and rectum.

Although about two years away from becoming widely available for public use, Mayo Clinic researchers believe this new method could significantly change the way screening for colorectal cancer is done. Most importantly, they think this new detection method may save thousands of lives annually.

Requiring a stool specimen, the EXACT detection method involves analyzing DNA that's shed from the surface of colorectal tumors and excreted in the stool. Measuring specific DNA abnormalities that are unique to precancerous polyps and early stage cancer results in high accuracy of detection.

"This new, non-invasive test safely and accurately detected curable-stage cancer of the colon and rectum," says David Ahlquist, M.D., a Mayo Clinic gastroenterologist and lead researcher on the study.

"Furthermore, the method detected precancerous polyps," says Dr. Ahlquist. "That's important because by detecting polyps and endoscopically removing them, we know that colorectal cancer can be prevented."

The next step is for the DNA colorectal cancer test to undergo another phase of clinical trials, scheduled to begin this January. Meanwhile, Mayo Clinic physicians encourage people age 50 years and older to follow their physicians' advice and the current recommendations for screening.

According to Dr. Ahlquist, the DNA colorectal cancer test shows promise for supplanting the fecal blood test, an often used but confounding screening test for finding blood in the stool.

"A major problem with the fecal blood test is that as many as 5 to 10 percent of the screened individuals have a false-positive, or incorrect, reading from the test," says Dr. Ahlquist. "This means that one in every 10 to 20 people screened has to unnecessarily undergo a colonoscopy, a costly and invasive medical procedure, to further evaluate the colon.

"Another problem with the fecal blood test is that blood in the stool is not present with many early stage colorectal cancers, nor with the vast majority of polyps," he added.

Colorectal cancer is the second leading cause of malignant death in the United States, accounting for more than 10 percent of all cancer deaths. Annually, 130,000 new cases of colorectal cancer are diagnosed. Over their lifetime, about one in 18 people gets colorectal cancer.

The EXACT scientists developed the technology for this new detection method, which includes novel techniques for recovering human DNA from stool and for measuring a number of tumor-specific DNA alterations.

The initial double-blind study involved analysis of DNA in stool specimens from 61 patients. Unknown to the EXACT scientists performing the test, 22 of the patients had been previously diagnosed with colorectal cancer, 11 of the patients had large pre-cancerous polyps and 28 of the patients had normal colons.

The new DNA colorectal cancer test detected 91 percent of the colorectal cancers and 73 percent of the polyps. There were no incorrect readings among any of the patients with a normal colon.

The collaborative study demonstrated the feasibility of DNA stool analysis as a screening approach and paved the way for a three-year clinical trial. The upcoming clinical trial will be funded by a $4.9 million grant from the National Cancer Institute. Dr. Ahlquist will lead the research effort and Mayo Clinic will be the principle site for the clinical trial.

The DNA colorectal cancer test has several patient-friendly features. An individual can provide a stool specimen in the privacy of their own home by using a special kit that fits on the toilet seat. The DNA test involves no dietary or medication restrictions. Furthermore, in contrast to all invasive screening methods used for colorectal cancer detection, no bowel preparation is needed for the test.

The DNA test also detects tumors and polyps throughout the entire colon, whereas sigmoidoscopy, another invasive detection method, inspects only the lower portion of the colon.

Although the up-front costs of the DNA colorectal cancer test are expected to be more than that of a fecal blood test, Dr. Ahlquist says that in the long run the DNA method could be more cost-effective.

"Because of the high rate of accuracy, the DNA colorectal cancer test could require fewer, unnecessary colonoscopies to be performed," he says. "That will mean a savings in health care expenses because having a colonoscopy in this country currently costs anywhere from $1,000 to $2,500."

He adds that "Costly operations to remove colorectal cancers also may be reduced if the new method leads to more effective detection of precancerous polyps."

"Most important, the new DNA colorectal cancer test has the potential to significantly reduce the morbidity and mortality of colorectal cancer," says Dr. Ahlquist. "Colorectal cancer is largely preventable and curable if detected early."
Laurel J. Kelly
Division of Communications
Ozmun East 6
Phone 507-538-1092
Fax 507-284-8713

Mayo Clinic

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