Among people at increased risk of colorectal cancer, computed tomographic (CT) colonography correctly classified 85% of the people with advanced adenomas or cancer and 88% of the people without advanced adenomas or cancer. These results were published in the Journal of the American Medical Association.
Colon cancer is the second leading cause of cancer death in the United States. If detected and treated early, colorectal cancer is highly curable. Screening for colorectal cancer is recommended starting at the age of 50 for individuals at average risk of developing the disease and earlier for those at higher risk. In addition to detecting cancer, colorectal cancer screening tests can also help identify adenomas (precancerous growths in the colon or rectum).
For individuals at increased risk of colon cancer as a result of personal or family history, colonoscopy is the recommended screening test. During the procedure, a lighted tube with an attached camera is inserted into the rectum and through the colon. The physician views the colon on a screen and is able to remove abnormal-looking areas or growths. Although colonoscopy is a highly effective screening tool, some patients are reluctant to undergo the procedure.
CT colonography is another screening test for colorectal cancer. The procedure requires the same bowel preparation as colonoscopy, but uses a computed tomography (CT) scanner to visualize the large intestine. The procedure is less invasive than colonoscopy (which may make people more willing to be screened), but individuals who are found to have colorectal growths will still need to undergo a traditional colonoscopy in order to have those growths removed. There is also some debate about the accuracy of CT colonography.
To evaluate the accuracy of CT colonography among individuals at increased risk of colorectal cancer, researchers in Europe conducted a study among 937 people. The study participants were considered to be at increased risk of colorectal cancer as a result of advanced adenoma or colorectal cancer in a first-degree relative (parent, sibling, or child); a personal history of colorectal adenoma; or a positive result from a fecal occult blood test (FOBT).
Study participants underwent both CT colonography and colonoscopy on the same day. Colonoscopy was considered to be the gold standard, and was the test to which CT colonography was compared. The study assessed the ability of CT colonography to detect colorectal growths (advanced adenomas or cancer) that measured 6 mm or larger.
- CT colonography detected 151 of the 177 people with advanced adenomas or colorectal cancer (the sensitivity of the test was 85%).
- Of the 760 people without advanced adenomas or colorectal cancer, CT colonography correctly classified 667 (the specificity of the test was 88%).
The researchers note that CT colonography may not be the best initial test for the subset of patients with positive FOBT. These patients have a relatively high rate of advanced adenomas, which means that many will require traditional colonoscopy. In addition, some measures of CT colonography performance were worse in this group of patients. Nevertheless, the researchers note that CT colonography may be an option for FOBT-positive patients who refuse colonoscopy.
The results of this study suggest that CT colonography may be an acceptable alternative to colonoscopy among people at increased risk of colorectal cancer as a result of personal or family history. CT colonography misses some colorectal growths, but may increase adherence to colorectal cancer screening guidelines.
Reference: Regge D, Laudi C, Galatola G et al. Diagnostic accuracy of computed tomographic colonography for the detection of advanced neoplasia in individuals at increased risk of colorectal cancer. Journal of the American Medical Association. 2009;301:2453-2461.
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