How Accurate is a Colonoscopy?Mar 31, 2014
Until recently, physicians thought a colonoscopy was 100 percent accurate. New research from the University of Utah’s Huntsman Cancer Institute shows it is not. Dr. N. Jewel Samadder talks about what the research discovered and what doctors and patients need to know to get the best result possible.
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Host: It's been generally thought that a colonoscopy was 100% effective at preventing colorectal cancer, but new research has shown that's not necessarily the case. N. Jewel Samadder is the lead author of a recent study. He's at Huntsman Cancer Institute. What did you learn in this study?
Dr. Samadder: Yes, for a long time physicians were under the impression that colonoscopy was 100% or nearly 100% protective from colorectal cancer, however, our data clearly shows that though colonoscopy is excellent, it can capture 94% of all colorectal cancer.
Host: That's still pretty good.
Dr. Samadder: Exactly, it's pretty good, but it's not perfect. We just need to be aware that it's not perfect. We need to figure out why this small number, 6% of all colon cancers, are being missed at colonoscopy, and what can we do to capture them.
Host: So what did you discover as far as why?
Dr. Samadder: We found a number of predictors that were associated with the missed colon cancers at colonoscopy. This included patients being of an older age, over age 65, having a family history of colorectal cancer in a close relative, or having a polyp, which is a precursor of colon cancer, found at the prior colonoscopy. These are some features that physicians can use to decide the risk that their patient may have for missed or interval colon cancer at colonoscopy. Hopefully that will allow them to spend more time examining the colon in these high risk patients and reduce the risk of missed cancers.
Host: So if you don't have those risk factors you're probably still going to be really good. If you do have those risk factors the physician actually can spend more time and overcome them?
Dr. Samadder: We think so. We think that, obviously, every physician should spend as much time as he or she needs to examine the colon and do a good job of reducing the risk of colon cancer in their patients, however, with patients who have these risk factors the physician can spend additional time in the colon. Some studies have suggested that the amount of time required to examine the colon should be at least six minutes, and some have suggested nine minutes or more. Physicians could elect to use a longer time on the withdrawal to examine the colon. They could also make sure that the bowel preparation is adequate so that they can look behind folds throughout the colon without stool impairing their vision.
Host: For patients it's really important that they communicate any of these risk factors to their physician so that they can have the information to do a more thorough job.
Dr. Samadder: They need to have an open discussion talking about their family history of colorectal cancer as well as the results of polyps, these precursors to colon cancer, that were found at a prior colonoscopy.
Host: This was a really significant study of a wide base of population if I understand correctly as well, so these results are very accurate.
Dr. Samadder: Yes, the data here which is derived in Utah is broadly applicable to the rest of the United States since the data was generated from both a very large academic medical center and a large managed care organization that together account for over 85% of all patient care in the State of Utah. It's broadly applicable throughout the United States. We hope that it will inform patients and physicians of the strength of colonoscopy in preventing colon cancer, but also the challenges that lie with colon cancer screening that not all cancers are detected at colonoscopy. Hopefully it will drive further research as to understanding the causes of these missed cancers, what we can do to better understand the limitations of colonoscopy and improve polyp detection and polyp removal to make colonoscopy maximally useful.
Host: What's the takeaway message that you would want to have our audience leave this discussion with?
Dr. Samadder: I think the take home message is that colonoscopy is extremely effective at reducing colorectal cancer, however, like any test it is not perfect. Up to 6% of colon cancers can be missed at colonoscopy, and it's important for patients and physicians to discuss some of the risk factors that we've found that can increase your chance of having a missed cancer including older age, having a family history of colorectal cancer and a prior colonoscopy with polyps or advanced polyps found.
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