Screening Strategies for Colorectal Cancer

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The summary below is from the full report titled "Cost-Effectiveness of Colonoscopy in Screening for Colorectal Cancer." It is in the 17 October 2000 issue of Annals of Internal Medicine (volume 133, pages 573-584). The authors are A Sonnenberg, F Delcò, and JM Inadomi.

What is the problem and what is known about it so far?

Cancer of the colon or rectum (colorectal cancer) is the second leading cause of death from cancer in the United States. Polyps are noncancerous outgrowths of the wall of the colon or rectum that can become cancerous. Screening tests prevent some colorectal cancers by detecting and removing polyps before they become cancers and by detecting cancers in their early stages, when they can still be cured with surgery. The available screening tests are fecal occult blood testing (FOBT), flexible sigmoidoscopy, and colonoscopy. Fecal occult blood testing uses a simple chemical reaction to detect blood hidden in stool. Since polyps and colorectal cancers can cause blood to leak into the stool, a positive FOBT suggests the need for further testing. Flexible sigmoidoscopy involves looking into the rectum and lower colon through a tube-shaped instrument; colonoscopy uses a similar but longer instrument to look at the entire colon. It is possible to take samples of the colon (biopsies) and remove polyps during both procedures. Fecal occult blood testing is inexpensive, colonoscopy is very expensive, and costs of sigmoidoscopy are somewhere in between. It is not clear which screening strategy makes the most sense in terms of costs and associated benefits.

Why did the researchers do this particular study?

To compare the cost-effectiveness of screening patients for colorectal cancer by using FOBT every year, flexible sigmoidoscopy every 5 years, or colonoscopy every 10 years, beginning at 50 years of age.

Who was studied?

Rather than studying actual patients, the researchers used a computer model to simulate what would happen to a "virtual" group of 50-year-old patients considering screening for colon cancer. They assumed that patients had no special risks for colon cancer, such as a positive family history.

How was the study done?

The researchers used information from actual patients to estimate what might happen when patients were screened by using the three strategies and how much each strategy would cost for each year of life it saves. They used these estimates in their computer model.

What did the researchers find?

Compared with no screening, yearly screening with FOBT prevents 18% of all colorectal cancers, sigmoidoscopy every 5 years prevents 34%, and colonoscopy every 10 years prevents 75%. Colonoscopy also results in more years of life saved. For each year of life saved, FOBT costs $81,678, sigmoidoscopy costs $74,031, and colonoscopy costs $28,143.

What were the limitations of the study?

This study was a computer simulation, so we cannot be sure what the results would be in actual patients. However, studies of this problem using actual patients are unlikely to be done soon (if ever).

What are the implications of the study?

Colonoscopy every 10 years beginning at 50 years of age is a more effective, and more cost-effective, way to screen for colorectal cancer than FOBT every year or sigmoidoscopy every 5 years.