Screening for Colorectal Cancer

Summary of Evidence

Evidence suggests that a decrease in mortality for colorectal cancer is associated with regular screening by sigmoidoscopy in people over the age of fifty. There is insufficient evidence to determine the optimum interval for such screening.

Significance

Colorectal cancer is the second leading cause of death from cancer in the United States. It is estimated that there were 138,200 new cases and 55,300 deaths in the U.S. in 1995. The incidence is increasing but the mortality rate is decreasing. The incidence is higher in men than in women 60.4 vs. 40.9 per 100,000 per year. There are groups that have a high incidence of colorectal cancer. These include those with heriditary conditions such as familial polyposis, familial nonpolyposis syndromes, the cancer family syndrome (autosomal dominant), heriditary site-specific colon cancer and ulcerative colitis.

Evidence of Benefit:

Sigmoidoscopy

A high percentage of early cancers can be detected by screening asymptomatic individuals over fifty years of age with a digital rectal examination, fecal occult blood testing, and sigmoidoscopy. Virtually all screening studies using these types of sigmoidoscopes have demonstrated an increase in early detection and a corresponding increase in survival compared to cases diagnosed in a nonscreening environment.

Fecal Occult Blood Test

In general, on initial examinations, from 1-5% of unselected persons tested with fecal occult blood tests have positive test results. Of those with positive test results, approximately 10% have cancer and approximately 20-30% have adenomas.

National trends show an increase in disease from 43% in 1973 to 32% in 1987. In addition, there has been an increase in survival and a decrease in mortality for colorectal cancer.

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