Colonoscopies Less Effective on Right Side of Colon (MedLine)

Director's Comments Transcript: Colonoscopy Effectiveness 02/02/2009

Greetings from the National Library of Medicine and MedlinePlus.gov Regards to all our listeners! I'm Rob Logan, Ph.D. senior staff National Library of Medicine substituting this week for Donald Lindberg, M.D, the Director of the U.S. National of Medicine. Here is what's new this week in MedlinePlus. To listen to Dr. Lindberg's comments, click here

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A colonoscopy helps detect cancer on the left side of the colon. But a recent Canadian study, published in the Annals of Internal Medicine, unexpectedly found colonoscopies are less effective at cancer screening on the colon's right side. Using a drawing of the colon on MedlinePlus'gov's colorectal cancer health topic page, the right side (also called the ascending colon) is the smaller of the colon's vertical regions. More information about MedlinePlus'gov's colorectal cancer health topic page is provided later in this podcast. In the case/control study, six Canadian researchers assessed patients between ages 52-90, who were diagnosed with colon cancer from 1996-2001. Using cancer registries and insurance claims forms (not medical records) kept by the Canadian province of Ontario, the researchers compared more than 10,000 persons, (who died of colon cancer by 2003) with more than 50,000 persons (who did not die of colon cancer). Incidentally, a diverse, international city (Toronto) is within the province of Ontario. Within the study's groups, the authors compared the chance of dying of colon cancer if one did or did not have a prior colonoscopy. The researchers were careful to compare groups of persons with similar age, sex, and socioeconomic status. So, the study's findings are generalizable to middle aged men and women. The study found a comprehensive colonoscopy was statistically significantly linked to a lower death rate of colon cancer – if the cancer was on the left side of a patient's colon. The study found colonoscopies successfully detected about 66 percent of cancers on the colon's left side of the study's population. However, the study also found a comprehensive colonoscopy was not associated with a reduction of death rates if cancer occurred on the colon's right side. As a result, the researchers concluded colonoscopies were less effective to screen for right-sided colon cancer. The study's authors noted the current findings substantiate some previous research, which suggested colonoscopies were more effective in detecting cancers on the left side of the large intestine. An editorial accompanying the study adds the findings were surprising because the effectiveness of screening on the left versus right side of the colon was not perceived to be as pronounced. The editorial notes the study's use of administrative rather than medical records makes it difficult to determine the extent that Ontario patients adequately prepared for a colonoscopy. Among other possible reasons, the editorial finds some differences might be explained by a tendency for polyps on the right side of the colon to be more difficult for physicians to detect. The accompanying editorial notes the overall mortality risk offered by colonoscopies is probably around 60 to 70 rather than 90 percent. Nevertheless, the editorial observes the study's findings do not challenge existing recommendations that men and women after age 50 should receive a colonoscopy to screen for colon cancer. In fact, the study's projected reduction of death rates is better than for many common cancer prevention screening procedures. As the headline of a New York Times editorial about the study said, colonoscopies remain (and we quote) 'not perfect, still essential" (end of quote). The study points out the need for physicians to be more forthcoming about a colonoscopy's limitations. Following the release of the findings, the New York Times reported the American Cancer Society and the U.S. Centers for Disease Control and Prevention are developing new measures to boost colonoscopy screening quality. MedlinePlus' colorectal cancer health topic page reports colorectal cancer ranks as the fourth most common cancer of men and women in the U.S. There are about 148,000 new cases of colon and rectal cancer each year (divided almost evenly between men and women), and about 50,000 persons die of the diseases annually. MedlinePlus' colorectal cancer health topic page explains colonoscopy screenings are important because at times patients have no symptoms of cancer of the colon or rectum. Some symptoms include: blood in the stool, narrower stools, a change in bowel habits, and general stomach discomfort. Screening helps physicians determine colon cancer early, which significantly improves a man or women's chances to recover. MedlinePlus' comprehensive colorectal cancer health topic page begins with an interactive tutorial about colon cancer. The interactive tutorial is narrated and contains helpful drawings. Its audio visual format is especially recommended for those who seek an easy-to-understand overview of colon cancer. Other interactive tutorials are available about: colon cancer surgery, and colonoscopy, among others. MedlinePlus' colorectal cancer health topic page includes information on:  diagnosis/symptoms, treatment, disease management, as well as alternative therapy. The health topic page's prevention and screening section contains links to information about the prevention, early detection, screening tests, and risk factors for colorectal cancer. Similar to the information found on other MedlinePlus health topic pages, the links to topics within this section are provided by highly reputable organizations, such as the National Cancer Institute, the American Medical Association, the American Cancer Society, and the Mayo Foundation for Medical Education and Research. There is additional information on MedlinePlus' colorectal cancer health topic page about: related financial issues, current clinical trials, the latest research, and specific information for women. To find MedlinePlus.gov's colorectal cancer health topic page, type 'colon cancer' in the search box on MedlinePlus' home page. Then, click on 'colorectal cancer (National Library of Medicine).