Colonoscopies Imperfect but Still Necessary

According to a recent study, colonoscopies failed to detect virtually every case of cancer in the right side of the colon.

The long-standing axiom regarding traditional colonoscopies has been that they detect 90% of colorectal cancers. A recent Canadian study found the percentage might actually be much lower, in the 60% to 70% range. According to the study, colonoscopies failed to detect virtually every case of cancer in the right side of the colon. The researchers noted that 40% of colon cancers arise in the colon’s right side.

Before oncologists and gastroenterologists begin to doubt the effectiveness of colonoscopies, David Kooby, MD, a surgical oncologist specializing in colon cancers at Emory University’s Winship Cancer Institute, advises caution when interpreting the new data. He noted it is a retrospective study. “We don’t know what the intent was of each colonoscopy beforehand. It’s impossible to know that in a retrospective study,” he said. Dr. Kooby said that even if one assumes that data from the study is “exactly right,” picking up 60% of cancers versus none still favors colonoscopy screening.

Benefit versus Risk

Dr. Kooby explained that in medicine, as in many sciences, there is no such thing as perfection, and he is concerned that patients already reluctant to have a colonoscopy will read about the study and use it as another reason not to have one.

Robert J. Green, MD, MSCE, an oncologist with Palm Beach Cancer Institute on the campus of Good Samaritan Medical Center, said he has already witnessed this phenomenon. “When the study came out, I had several people say to me, ‘Wait a second. I just read that colonoscopy is not nearly that good,’” said Dr. Green. He compared the 60% detection rate afforded by colonoscopy to the 25% rate of breast cancers detected with mammography. “It’s pretty hard to find people who say, ‘I don’t think I want to do my mammogram.’” Dr. Green said the study’s take-home message should be that colonoscopy is imperfect, but “imperfect doesn’t mean bad.”

Thomas Weber, MD, with Montefiore-Einstein Cancer Center, founder and president of the Colon Cancer Challenge Foundation, acknowledged that there are risks associated with traditional colonoscopy, such as bleeding or injuring the colon. Dr. Weber pointed out that the benefits of colonoscopy far outweigh the risks, and pointed out that “if you compare the number of polyps removed and potential cancers prevented and lives saved, it exceeds the risk of injury.”

Alternative Screening Technologies

Virtual colonoscopy is a newer screening procedure that uses computed tomography scanning to image the inside of the colon. There is growing support for the procedure, but Dr. Green said virtual colonoscopy has its share of limitations. It requires the same bowel preparation as traditional colonoscopy, which is one of the things patients most detest about the procedure. Should virtual colonoscopy detect a polyp, the patient must often undergo a biopsy using traditional colonoscopy.

A second technology mentioned in the American Cancer Society’s guidelines for colorectal cancer screening is DNA stool testing. This procedure looks for DNA abnormalities that might indicate advanced polyps or malignancy. Although promising research has been conducted in this area, said Dr. Green, it is not yet ready to replace traditional colonoscopy as the screening standard. “[Colonoscopy] is still a really good test,” he said. “It’s far and away the best test that we have for finding and preventing the disease early.” He noted that findings from the new study would not change his message to patients, which is that “people for whom colonoscopy is appropriate ought to have one.”

Role for Oncologists

Dr. Weber said community oncologists are on the front line in terms of reminding patients and families that if someone in the family is affected with colorectal cancer, other family members are at increased risk for the disease. “Community oncologists have a tremendous opportunity to promote awareness of the value of screening and surveillance for families that have been affected [by colorectal cancer],” Dr. Weber said. “I think one of the most important things we can all do, doctors and patients, is to really talk to each other about family history and identify people who are at increased risk.” The American Cancer Society recommends colonoscopy screenings at age 40, or 10 years prior to the age of the earliest case detected in a family.

Dr. Green said promoting diligent bowel preparation is one of the keys to improving the accuracy of colonoscopy. He noted that the recent study indicated most cancers missed were on the right side of the colon; this is a harder area to prepare and it is the first place secretions begin to gather following bowel evacuation. “When you don’t have a good prep, the area more likely to suffer is in the right colon. That’s why it’s so important to do the prep correctly and be pretty meticulous about following the instructions.” Some physicians recommend drinking half of the preparation the night before and the remainder the morning of the procedure to ensure that the bowels are clean.

Study Limitations

It is important to note that cancers arising on the right side of the colon are more likely to be flat, indented, or serrated lesions, which are harder to detect. They are also associated with malignancies that are more aggressive. Raised polyps occur more often on the left side, which may contribute to the greater rate of detection of left-sided cancers. In the Canadian study, colonoscopies were performed by the patient’s physician rather than urologists who specialize in performing colonoscopies, which is more typical in the United States. This may affect applicability of the results outside of Canada.

Ed Rabinowitz is a veteran healthcare writer and reporter. He welcomes comments at edwardr@frontiernet.net.

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