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Is screening for bowel cancer effective?

The simple answer is yes! There are two components of screening.

(February 2001; updated November 2001)

(1) Testing for subtle intestinal bleeding. This should be done yearly. Healthful Life suggests starting at age 45, others wait until age 50. The test is easy to perform. It can be done by taking a cotton swab on the end of an applicator (similar to what you would use to clean wax from your ear) and applying it in the anal area after a bowel movement (before using toilet paper). The stool material is then put on specially prepared slides. This is done in duplicate after three successive bowel movements. The slides are then promptly returned to your physician or to a laboratory for testing. Alternatively, there are home test kits with a specially prepared paper you drop into the toilet bowel after a bowel movement (before flushing). If a color change occurs, it suggests blood. Then, you go to your health care practitioner for a repeat test using the specially-prepared slides.

To prepare for the test, you should not be on aspirin for several days (it can cause bleeding) and should be on a diet with a good deal of roughage which is used to get cancers or benign growths that could become cancerous to bleed. Your health care practitioner will help with the instructions. If blood is found, it warrants a full work-up with colonoscopy (a flexible tube) or appropriate x-rays.

(2) A lower bowel examination by a specially trained health care provider to look directly at the bowel with a flexible tube. For most people, an examination that visualizes the left side of the colon is recommended to detect and remove non-cancerous growths (polyps) that could turn to cancer or to detect cancer in its earliest stages when the cure rate by surgery is very high. Healthful Life recommends the left-sided examination be done every five years starting at age 45 (others wait until age 50).

Some gastroenterologists and cancer specialists want to do the more extensive full colonoscopy so they can see the whole lower bowel. The left side visualizes the lowest 60 centimeters (about 25 inches) of the colon; full colonoscopy visualizes approximately 160 centimeters (about 60 inches). That is ideal, but is more time consuming and requires more expertise. Examination of the left side should be virtually risk free; doing the entire colon, going from the left side across the middle to the right side, carries a small risk of bowel perforation and hemorrhage. That being the case, only a real expert should be entrusted with the examination. If a polyp is found in the left side, a full colonoscopy is obligatory because, in that situation, there is a strong possibility of a polyp on the right side.

Why is a full colonoscopy better? Because the left-side examination misses from 20 percent to 30 percent of polyps that could develop into cancer.

There are more than 155,000 new cases of bowel cancer every year, and more than 55,000 deaths. The combination of yearly tests for subtle bleeding and colon examination every five years will cut the likelihood of invasive bowel cancer or death from bowel cancer by at least one-half - that is very good.

Could the left-sided bowel examination with a flexible instrument be done less frequently - say every seven or every ten years. The answer is probably yes, but that has not been adequately studied.

In July 2000, two studies of full colonoscopy appeared in The New England Journal of Medicine. Both studies and an accompanying editorial say a significant percentage of polyps that might become cancerous are missed by left-sided colonoscopy; therefore, they recommend full colonoscopy.

In the two studies of 5,115 men and women who underwent full colonoscopy, a total of 467 polyps or early cancers were found. Twenty-one percent (90) would have been missed by doing only left-sided colonoscopy.

Looked at another way, in less than two percent of the 5,115 persons studied, polyps that could turn into cancer were missed by doing only left-sided colonoscopy.

The studies did not include studies to determine how many of those 90 polyps would have been detected by the Hemoccult tests Healthful Life does every year. It is well known that a significant percentage of polyps in that location bleed and, therefore, can be detected by Hemoccult tests.

The studies were primarily focused on polyps that could become cancerous, not on cancer. It is not known what percentage of the polyps would eventually become cancerous and what percentage would never progress that far; it is known that most polyps never turn to cancer.

It is, therefore, virtually certain that some of those polyps missed by doing only left-sided colonoscopy would have been detected by the annual Hemoccult tests and a significant percentage would never have progressed to cancer.

The editorial indicates that full colonoscopy will result in the dangerous complication of perforation "in less than 0.2 percent of examinations performed by experienced gastroenterologists". In the larger of the two studies, serious bleeding or other complications (not perforation) occurred in 0.3 percent of the full colonoscopy examinations.

Add those together and the serious complication rate of full colonoscopy is likely to be in the 0.5 percent range. Because the overwhelming majority of persons undergoing colonoscopy will have normal findings, most of these complications will occur in those with normal examinations.

The costs of full colonoscopy are far greater-$500 to $2,400 for full colonoscopy; in the $150 to $300 range for left-sided colonoscopy. It also takes two to three times as long to do a full colonoscopy compared to the left-sided colon examination, and it causes more discomfort during the procedure.

If full colonoscopy were done every ten years for 100 million persons (a number that would increase markedly every decade as our population ages), it would be inevitable that an ever-increasing percentage of the examinations would be done by less experienced gastroenterologists or other health care personnel (especially in more rural or less populated areas). That would result in an increased complication rate.

Another article in the August 2001 issue of The New England Journal of Medicine also supported full colonoscopy.

For now, the less dangerous and much less expensive left-sided colonoscopy plus yearly tests for subtle bleeding is our recommendation, but full colonoscopy is a perfectly good alternative. For those who have a full colonoscopy, even though there is no direct evidence, the recommendation by several expert groups is a full colonoscopy every ten years.

Why does Healthful Life start screening earlier than other experts? The answer is that the frequency of bowel cancer starts increasing after age 40. There are about 8,000 new cases each year between ages 40 and 49. The increase in frequency is much greater after age 50. Many of the cancers first detected between ages 50 and 59 started before age 50, so it seems reasonable to find these cancers and polyps that could become cancerous by screening between ages 40 and 49. Besides, starting screening at age 50 will not help the 7,000 cases diagnosed each year in those ages 40 to 49; most of these can be prevented or caught so early they can be cured by following our Program.

Winawer, S.J. Colorectal cancer screening: Guidelines and rationale. Gastroenterology. Vol 112. Pgs 594-642. 1997.

Lieberman, D.A., et al. Use of colonoscopy to screen asymptomatic adults for colorectal cancer. The New England Journal of Medicine. Vol 343 (July 20) Pgs 162-168. 2000.

Imperiale, T.F., et al. Risk of colorectal proximal neoplasms in asymptomatic adults according to distal colorectal findings. The New England Journal of Medicine. Vol 343. (July 20) Pgs 169-174. 2000.

Lieberman, D.A. and Weiss, D.G. One time screening for colorectal cancer with combined fecal occult blood testing and examination of the distal colon. The New England Journal of Medicine. Vol 345 (August 23) Pgs 555-560. 2001.

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