Colonoscopy Health Article

Morbidity and mortality rates

In 2003, an estimated 57,100 people will die from colorectal cancer. Although screening could find precancerous growths (polyps), which lead to colorectal cancer, screening rates in the United States remain low. Removing polyps before they turn into cancer could prevent the disease and potentially reduce deaths. Scientific evidence shows that more than one-third of deaths from colorectal cancer could be avoided if people aged 50 years and older were screened regularly.

Despite recent advances in screening and treatment for colon cancer, it is still one of the most common cancers among men and women in the United States. According to a report in the American Journal of Gastroenterology, there has been no improvement in colon cancer survival in the United States since the 1980s. As well, the number of patients surviving five years after their cancer diagnosis did not improve.

Recent National Cancer Institute-funded clinical trials show that taking daily aspirin for as little as three years could reduce the development of colorectal polyps by 19–35% in people at high risk for colorectal cancer.

The Center for Disease Control and Prevention recommends that everyone 50 years of age and over have one or a combination of the four recommended screening tests: fecal occult blood test, sigmoidoscopy, colonoscopy, or barium enema.

Alternatives

New research suggests that a simple blood test may identify people at risk of colorectal cancer. The blood test detects a genetic alteration that may identify people who are likely to develop the disease and who would benefit from additional screening; however, further research has to be done before this test becomes available.

Virtual colonoscopy is a new technique under development and evaluation for screening for colon polyps and cancer, and is undergoing continual improvement. One technique uses images from a magnetic resonance imaging (MRI) scan, and the other uses the x-ray images from a computerized tomography (CT) scan. They both provide views of the colon that are similar to those obtained in a colonoscopy. The images of the colon are produced by computerized manipulations rather than direct observation through the colonoscope.

While the CT scan technique is available in many radiology units, the MRI scan technique is still experimental. The colon is cleaned out using potent laxatives for both types of studies. A virtual image of the colon is formed after the scans are performed, and the images are analyzed and manipulated.

One benefit of the CT scan is that it can find polyps that occasionally are missed by colonoscopy because the polyps lie behind folds within the colon. Nevertheless, criticisms of the CT scan include:

• It cannot find small polyps (<0.2 in [5 mm] in size) that are easily seen in a colonoscopy.
• It is less able to find flat polyps compared to a colonoscopy.
• The procedure does not require patients to be sedated or put under anesthesia, and it can be performed in less than one minute, compared with about 30–60 minutes, plus recovery time required for standard colonoscopy.
• Small pieces of stool can look like polyps on the CT scan and lead to a diagnosis of polyp when there is none.
• If colonic polyps are found by virtual colonoscopy, then standard colonoscopy must be done to remove the polyps. As a result, the individual must undergo two procedures.

Although the CT scan is a good option for individuals who cannot or will not undergo standard colonoscopy, it has not been determined if it should be a primary screening tool for individuals at either normal risk or high risk for polyps or cancer.

BOOKS

Beers, Mark H. and Robert Berkow, eds. Merck Manual of Diagnosis and Therapy, 17th edition. Whitehouse Station, NJ: Merck & Co., 1999.

Dachman, Abraham H., (editor). Atlas of Virtual Colonoscopy. Berlin: Springer Verlag, 2003.

Dafnis, George. Colonoscopy: Introduction and Development, Completion Rates, Complications and Cancer Detection (Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, 1039). Uppsala, Sweden: Uppsala University, 2001.

Tierney, Lawrence M., Stephen J. McPhee, and Maxine A. Papadakis (editors). Current Medical Diagnosis & Treatment 2003. Stamford, CT: Appleton & Lange, 2002.

PERIODICALS

Dominitz, J. A., et al. "Complications of Colonoscopy." Gastrointestinal Endoscopy 57, no 4 (April 2003): 441–5.

Isenberg, G. A., et al. "Virtual Colonoscopy." Gastrointestinal Endoscopy 57, no 4 (April 2003): 451–4.

Rabeneck, Linda, Hashem B. El-Serag, Jessica A. Davila, and Robert S. Sandler. "Outcomes of Colorectal Cancer in the United States: No Change in Survival (1986–1997)." The American Journal of Gastroenterology 98, no 2 (February 2003): 471–477.