• Flat lesions in colon deadlier, harder to detect than polyps

    July 2008

    The current U.S. medical practice of focusing on polyps in screening for colon cancer was called into question recently by the results of the largest colonoscopy study of its kind. A team of researchers at the Veterans Affairs Palo Alto Health Care System examined more than 1,800 patients for nonpolypoid colorectal neoplasms (NP-CRNs). They wanted to find out whether NP-CRNs – slightly elevated, completely flat or slightly depressed lesions – were more prevalent and dangerous than previously thought.

    Related information: New stool test shows promise  |  Colonoscopy  |  Markey Cancer Center

    Most colorectal cancers are believed to develop over time from polyps, which are usually detected by routine screening colonoscopy. Previously, U.S. doctors considered NP-CRNs to be a problem primarily in Japan. Although Japanese researchers became concerned about these flat lesions in the 1980s and 1990s, data about these lesions in the United States have been limited.

    Flat lesions in the colon are harder to detect than polyps and may be more likely to become cancerous. 

    Typically, these flat lesions are harder to detect than polypoid lesions, and only a well-trained, vigilant clinician can see and remove them. If any stool is left in the bowel before colonoscopy, NP-CRNs may be completely hidden. The results of recent U.S. studies suggested these lesions may be more common in this country than previously believed and may be more likely than other polypoid lesions to become cancerous.

    Screening for colon cancer

    Colon cancer is the second leading cause of cancer deaths in the West; it results in approximately 52,000 deaths each year in the United States. Unlike most other cancers, colon cancer is totally preventable if the precancerous growths are found and removed. Because colon cancer usually grows slowly, screening colonoscopy is most often performed at 10-year intervals for patients older than 50 years and for younger patients who have a family history of the disease.

    During a colonoscopy, a gastroenterologist or colorectal surgeon evaluates the appearance of the inside of the colon (large bowel) by inserting into the anus a flexible tube that is about the thickness of a finger. The tube, which contains a tiny video camera, is advanced slowly into the rectum and through the colon. The clinician can visualize the colon either by looking through the instrument or by viewing the live video feed on a TV monitor. Most patients are fully sedated during the procedure.

    How the study was conducted

    The California study involved male veterans who underwent colonoscopy for screening, surveillance or evaluation for symptoms of possible colorectal cancer. Most patients were white with an average age of 64 years. This was the largest group of non Asian patients to be evaluated for NP-CRNs to date. The results of the study were published in the March 5, 2008, issue of JAMA, the journal of the American Medical Association.

    “The elephant in the endoscopy suite is missed lesions.”
    – David Lieberman, MD

    To become proficient in diagnosing NP-CRNs, doctors in Palo Alto developed a faculty exchange program with leading Japanese endoscopy centers in early 1999. Armed with this new expertise, they conducted their study from July 2003 through June 2004.

    Patients took four liters of polyethylene glycol solution and one 296-mL dose of sodium phosphate solution orally the night before their exam. The colonoscopies were performed by four board-certified gastroenterologists using standard endoscopic equipment. An indigo carmine spray was used to highlight the lesions if necessary.

    Study findings

    Doctors found that 9.35 percent of the men had flat lesions, and these lesions were more than five times more likely than other polyps to contain cancer or precancerous tissue. Although these lesions accounted for only 15 percent of the potentially cancerous growths, they were involved in half of the cancers.

    The improved detection of NP-CRNs could lead to prevention of more colorectal cancers, the researchers said. Between 0.3 and 0.9 percent of patients who have colonoscopies will be found to have cancer within three years after the procedure. It is possible that missed lesions contribute to this percentage.

    In an editorial accompanying the study, David Lieberman, MD, head of gastroenterology at the Portland VA Medical Center, wrote, “The elephant in the endoscopy suite is missed lesions. There has been increasing recognition that colonoscopy, even by experienced and well-trained endoscopists, may fail to detect important colon pathology.”

    Previous studies have shown that CT scans are 90 percent successful in finding colon polyps. But because CT scans use X-rays to reveal shapes that protrude, it is unlikely that current CT technology can detect flat lesions.

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Page last updated: 8/7/2015 1:06:28 PM
  • What the news means for you

    Good colon preparation is key to successful test

    Patrick Mosler, MD

    Wright, Heather, MDSeveral issues occurred to me with regard to this study. The first is the way the authors define a flat or nonpolypoid colorectal neoplasm – one whose height is half of its diameter. Using these criteria, doctors might classify many small polyps as “flat,” but in most cases these lesions are probably all lumped together as “small polyps” and removed. Therefore, the number of flat polyps that are found and adequately removed during screening colonoscopy in the United States may be underestimated.

    “A doctor can’t find a small or flat lesion if the colon isn’t clean enough.” 

    The second is the issue of colon preparation. There are still too many patients whose preparation before colonoscopy is not good enough. A doctor can’t find a small or flat lesion if the colon isn’t clean enough. So the most important thing to do is to make sure the colon is clean; then we can focus on finding small lesions.

    In this study, two different preparations were used instead of just the single preparation that is used for most colonoscopies. It makes sense, if you’re doing research, to have a very clean colon, but that’s not always the case in reality. Along with the bowel preparation given the night before, the researchers also sprayed a special dye in the colon to highlight lesions and ensure complete removal, a procedure that isn’t used in standard practice.

    At the University of Kentucky, we are defining factors that contribute to suboptimal bowel preparation. One of the most important factors is patient education, because good data show that almost any available preparation works if taken correctly. In addition to the usual two liters the night before the procedure, we’re now offering a new regimen of one liter of solution the night before, followed by another liter six hours before the procedure.

    Many studies have shown that this split dose regimen may be better than the single dose in preparing the colon for colonoscopy.

    Physician expertise

    Another important issue raised by this study is its reminder to doctors to look for these flat lesions. I don’t think you necessarily have to use any advanced techniques to find most of them. The first step is just to think about finding them.

    Colonoscopy should be performed in a center that specializes in such procedures. At the UK Digestive Health Program, we perform an average of 2,700 colonoscopies a year.

    If patients have concerns about the thoroughness of their colonoscopy, they can ask to see the colonoscopy report. They should ask whether the colon was clean enough, whether the doctor was able to see everything and whether the entire length of the colon was examined. Clinicians should routinely discuss these issues with a patient after the procedure.

    If the doctor can’t see the entire colon because of scar tissue, adhesions or other conditions that prevent a full colonoscopy, the patient needs to return for another test, such as virtual (CT) colonoscopy. This is the second-best test, but it’s not good enough for first-line screening, especially in detecting small or flat polyps.

    A new imaging technology that holds promise is narrow-band imaging. Narrowband imaging works by filtering the white light emitted by the endoscope and allowing only blue light with a narrower wave length to illuminate the colon. The blue light provides a greater visual contrast of the surface structure of the intestine.

    “If the doctor can’t see the entire colon because of scar tissue, adhesions or other conditions that prevent a full colonoscopy, the patient needs to return for another test, such as virtual (CT) colonoscopy. This is the second-best test.” 

    The UK Endoscopy Center plans to implement narrow-band imaging in colorectal cancer screening during the coming year. Once we have the new technology, we will be able to use it immediately. We plan to carry out research studies comparing this new imaging method to the current white-light technology for different indications.

    Seriousness of colon cancer

    Most health insurance, including Medicare, covers colorectal cancer screening performed according to current guidelines – screening colonoscopy every 10 years for patients older than 50 years and more often if abnormalities are found. Colonoscopy is very useful because most neoplasms don’t become cancerous for five to 10 years. If the patient comes in soon enough, we can find and remove a polyp before it becomes cancerous.

    In Western countries, colon cancer is the second leading cause of cancer deaths. However, fewer than 40 percent of people who are eligible for colorectal screening have this test, many because they have no insurance. Unfortunately, there is also a shortage of gastroenterologists, so even if the number of screenings doubled, we would have difficulty handling them.

    Dr. Mosler is a gastroenterologist in the UK Digestive Health Program and an assistant professor of digestive diseases in the UK College of Medicine.

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