Digestive Diseases News
Fall 2008

NDDIC Coordinating Panel Speaker Urges Early Detection of Colorectal Cancer

Early detection is critical for survival of colorectal cancer (CRC), the third leading cause of adult death in the United States, according to Michael B. Wallace, M.D., M.P.H., professor and vice chairman of medicine at the Mayo Clinic in Jacksonville, FL. Wallace, who spoke at the National Digestive Diseases Information Clearinghouse (NDDIC) annual Coordinating Panel meeting in June, said researchers expect that 150,000 diagnoses and 50,000 deaths will be attributed to CRC in 2008.

As with other cancers of the digestive system, the survival rate for early diagnosed CRC is stage dependent, according to Wallace. The 5-year survival rate for localized CRC is 90 percent, which is why raising awareness of early detection as an effective prevention strategy is so crucial. In most cases, CRC arises from an adenomatous polyp, a definable and detectable precancerous lesion, Wallace said. Detection and removal of a precursor lesion effectively treats the disease.

Small colon polyps and flat polyps, which may be more aggressive, present a challenge to the longstanding assumption that colonoscopy will detect all polyps and colon cancers, explained Wallace. Studies using repeat colonoscopy showed the overall “miss” rate to be 26 percent for small polyps, most of which are of unclear clinical significance.

The importance of small polyps and whether to inform patients of their presence are topics of discussion within the medical community. A study of small polyps removed during colonoscopy showed 69 percent to be adenomatous. Current standard practice with colonoscopy is to report all adenomatous polyps regardless of size and to base surveillance intervals on the number and size of adenomas.

A study at the Veterans Affairs Hospital in Palo Alto, CA, identified a new category of flat polyps previously recognized in Japan. The study found flat polyps were present in 9 percent of colonoscopies. Flat polyps had a tenfold increase in the likelihood of being cancerous, regardless of size.

Because flat polyps often go undetected, inspection techniques using chromoendoscopy and narrow band imaging were used to find them. Flat polyps were highlighted using blue dye for easier detection. Using endoscopic resection, polyps were injected with fluid to raise them for removal. These techniques are effective and safe but require specialized training.

Joint Guidelines

Wallace said, in recent months, the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology released Joint Guidelines for Early Detection of Colorectal Cancer and Adenomatous Polyps: 2008. The guidelines recommended

• tests to detect cancer. These tests involve stool analysis and are minimally invasive:

  • fecal occult blood test or guaiac—recommended every year after age 50.
  • fecal immunochemical tests.
  • stool DNA, a new test recommended every 5 years after age 50. The test analyzes DNA integrity and identifies gene mutations in the progression from adenomas to cancer. Stool quantity and shipping requirements make the test hard to do at home. Although studies show variable test performance, the stool DNA test’s sensitivity is superior to the guaiac test. More recent versions show improved accuracy, although invasive tests are better at detecting precancerous polyps. Combining both guaiac and stool DNA tests may result in improved program accuracy.
    
    

• tests to detect both cancerous and precancerous polyps. Only flexible sigmoidoscopy and colonoscopy can also treat polyps. These tests are more invasive:

  • barium enema.

  • computerized tomography (CT) colonography, also known as virtual colonoscopy. This test is a new recommendation, although this breakthrough “noninvasive” technology is not completely noninvasive. The test involves a CT scan with oral contrast, and the recommended bowel prep is similar to that of a standard colonoscopy. Patients show only minimal preference for CT colonography over standard colonoscopy and prefer to be asleep during the test. Meta-analyses have shown that overall accuracy for detecting large polyps—greater than 10 millimeters (mm)—is reasonably good; however, for all polyps, sensitivity is variable. Accuracy is poor in small polyps—smaller than 5 mm. Overall, standard colonoscopy is more accurate in detecting both small and large polyps. If polyps are found during CT colonography, a colonoscopy is needed for polyp removal; cost implications are an issue.

With a wide range of technology available for CRC detection and colon polyp removal, there are tradeoffs between accuracy and invasiveness, Wallace noted. Research priorities include estimating progression time from small polyps to CRC, improving technologies and techniques to eliminate cases of missed polyps and adenomas, and improving the accuracy of noninvasive, low-cost, acceptable screening tests.

The NDDIC has a fact sheet in English and Spanish entitled Colon Polyps: What You Need to Know. To see a copy, go to www.digestive.niddk.nih.gov/ddiseases/pubs/colonpolyps_ES.

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NIH Publication No. 09–4552
December 2008