Colonoscopies vs. DNA signatures to diagnose colorectal polyps

The new Cologuard test requires no bowel preparation, medication restriction or diet change.

APRIL 13, 2014 05:09

hospital doctors health 311 (photo credit: Ariel Jerozolimski [file[) — hospital doctors health 311

(photo credit: Ariel Jerozolimski [file[)

People over 50 (or younger, if there is a family history) know they have to undergo a colonoscopy periodically to find and eliminate precancerous growths in the colon to prevent the development of deadly colon cancer.

But they find it scary just to think about it and unpleasant to prepare for it – even though most who go through with it said it was really “no big deal.”

A clinical trial whose results were recently published in the prestigious New England Journal of Medicine (NEJM) on a promising test called Cologuard, for benign polyps and colorectal cancer has aroused much excitement among patients and gastroenterologists. Cologuard, a non-invasive sDNA test on stool samples, was co-developed by Mayo Clinic and Exact Sciences. Ordinary stool-sample tests routinely given in Israel look for blood, which can sometimes be a sign of colorectal cancer, but there are many false negatives and false positives.

In the new test, stool samples are analyzed for DNA signatures of precancer or cancer. The samples are easily collected and mailed from home, and the test requires no bowel preparation, medication restriction or diet change.

The clinical trial, called the DeeP-C study, included 10,000 patients at 90 medical centers throughout North America.

“Cologuard detection rates of early stage cancer and high-risk precancerous polyps validated in this large study were outstanding and have not been achieved by other noninvasive approaches,” says the study’s author, Dr. David Ahlquist, a Mayo Clinic gastroenterologist and co-inventor of the Cologuard test. “It is our hope that this accurate and user-friendly test will expand screening effectiveness and help curb colorectal cancer rates in much the same way as regular Pap smear screening has done for cervical cancer.”

Sensitivity of Cologuard for cancer was 92 percent overall, and 94% for the earliest and most curable cancer stages (stages I and II). Sensitivity was 69% for pre-cancerous polyps at greatest risk to progress to cancer. “The most important finding of the study is the high sensitivity of Cologuard for curable stage colorectal cancer, which represents the highest sensitivity of any noninvasive test to date,” said internal medicine specialist Dr. Thomas Imperiale of Indiana University Medical Center and a study author.

Colorectal cancer is often considered the most preventable, yet least prevented, cancer. Nearly half of adults over 50 and older have not been screened as recommended and, as a result, colorectal cancer has become the second- leading cause of cancer death in the developed world.

Cologuard works by testing a patient’s stool for altered DNA shed during digestion. Altered DNA is known to occur within colorectal cancers and precancerous polyps. The test also examines the stool for the presence of blood, another possible indicator of colorectal cancer. Combining the data from the stool DNA test and the blood test into a single result provides a comprehensive, powerful screening approach, which is reflected in the study results.

Because of its accessibility and ease of use, researchers hope the test will increase the number of people who will choose to be screened for colorectal cancer.

Asked to comment, veteran Jerusalem gastroenterologist Prof. Samuel Adler of the Bikur Holim campus of Shaare Zedek Medical Center, commented: “Yes, I have been following the DNA saga. It makes perfect sense; the change in colonic mucosa to neoplastic tissue (creating polyps and then tumors) is initiated by changes in DNA. Finding these changes and then defining who needs colonoscopy makes a lot of sense.”

Adler noted that the 92% sensitivity rate is impressive and if the specificity is high as well, it would make Cologuard a good screening test. It is a significant problem, however, that the test misses 31% of patients with high-grade dysplastic polyps. So it may be effective in reducing colorectal cancer mortality but be less effective in preventing colon cancer development by missing out on 31% of dangerous polyps.”

He concluded that it would be great if this test encourages the public to go for it, but I am worried about the cost.

“The bottom line is that colonoscopy is cheap in Israel and still superior to any non-invasive testing. But certainly, the future lies in DNA testing.”