Although largely preventable by the early detection and removal of adenomatous polyps, colorectal cancer (CRC) is the second leading cause of cancer deaths in the United States. In March, the American Cancer Society, the American College of Radiology, and the U.S. Multi-Society Task Force on Colorectal Cancer released the first joint consensus guidelines for detection of adenomatous polyps and CRC screening for asymptomatic adults age 50 years and older.

The new guidelines attempt to provide improved guidance about test characteristics and quality and delineate the differences between screening options by making a distinction between two categories of tests. The first category is partial or full structural exams (exams of the colon itself) that are effective in preventing CRC by discovering precancerous growths and allowing for their removal before they become malignant. The tests in this category require some patient preparation, must be done at a health care facility, and are somewhat invasive. The second category is fecal/stool laboratory tests primarily effective in detecting existing cancer. These tests require no preparation and may be collected or tested at home but must be done more frequently to be effective.

One other difference between screening options included in the guidelines (listed below) is that direct examinations such as sigmoidoscopy or colonoscopy allow for removal of polyps at the time the test is done. All other tests must be followed up with another procedure to remove any suspected growths. For additional details about the various tests, see the table on Colon cancer.

Structural exams that detect polyps and prevent cancer and recommended intervals for screening:

flexible sigmoidoscopy - every 5 years, or

colonoscopy - every 10 years, or

double contrast barium enema (DCBE) every 5 years, or

computed tomography colonography (CTC, see below) every 5 years.

Laboratory tests that primarily detect cancer and recommended intervals for screening:

guaiac-based fecal occult blood test (gFOBT) - annually

fecal immunochemical test (FIT) - annually

stool DNA test (sDNA, see below) - interval uncertain at this time

The new guidelines include two new tests: the stool DNA (sDNA) and computed tomography colonography (CTC), or virtual colonoscopy. They are included in the new recommendations to increase the number of screening options available to patients.

With the new tests added to the lists, patients and providers now have seven screening options available to them. Even so, it is the strong opinion of the panel issuing these guidelines that CRC prevention rather than cancer detection should be the primary goal of screening. The panel acknowledges, however, that patient preferences and availability of resources influence their selection of screening methods. Therefore, the guidelines are designed to help patients make an informed decision about their screening choices by understanding the strengths and limitations of each option.

The two new tests included in the guidelines are:

Computed Tomography Colonography: The CTC, or virtual colonoscopy, is a less invasive structural exam. Unlike the conventional colonoscopy, sigmoidoscopy, or the barium enema, the CTC does not require rectally inserting a camera-tipped tube or filling the colon with liquid barium. Rather the CTC combines CT imaging and computer software to form three-dimensional images of the colon, large intestine, and the lower end of the small intestine. While faster and more comfortable for patients than the three other structural screening tests, currently insurers do not cover the cost of the virtual colonoscopy.

Stool DNA: The sDNA test isolates DNA from a stool sample and analyzes it for markers known to be associated with CRC. The sDNA test requires collection of stool samples and, like the immunochemical tests, offers an advantage of needing no special dietary or other preparations prior to collecting the sample.

Evidence shows that screening asymptomatic individuals over age 50 for CRC can help detect early cancer and, for those methods that involve imaging, can detect precancerous lesions, enable their removal, and prevent cancer. The hoped-for outcome of the new guidelines and the addition of the two new testing options is an increase in the number of patients screened for CRC, an increase in the detection of adenomatous polyps, and a reduction in the number of CRC deaths nationwide. If you are age 50 or older, consult with your health care provider about your options and discuss which test may be right for you.

Sources
S1
ACS (March 5, 2008). Screening and Surveillance for the Early Detection of Colorectal Cancer and Adenomatous Polyps, 2008: A Joint Guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. (Abstract). On the Internet: http://caonline.amcancersoc.org/cgi/content/full/CA.2007.0018v1.

S2
ACS Website (March 5, 2008). Health Groups Issue Updated Colorectal Cancer Screening Guideline. On the Internet

S3
Grady, Denise. Two Tests Added to Recommended List to Prevent or Detect Colorectal Cancer. New York Times March 6, 2008. On the Internet: http://www.nytimes.com

S4
National Digestive Disease Information Clearinghouse/NDDIC: Virtual Colonoscopy (March 12, 2008). On the Internet: http://digestive.niddk.nih.gov/ddiseases/pubs/virtualcolonoscopy/