Screening for colorectal cancer.

Colorectal cancer remains a major cause of mortality in the United States. Of all persons diagnosed with this tumor, less than 50 percent survive five years. Useful preventive measures have not been established. Screening programs, however, offer the prospect of detecting cancers early in their course, when the prognosis for survival is more favorable. To date, no screening test has clearly demonstrated its effectiveness in reducing mortality from colorectal cancer. Periodic rigid sigmoidoscopy and stool occult blood testing have gained many advocates, but have yet to be proved worthwhile in adequately controlled clinical trials. Uncontrolled studies indicate that both these techniques discover approximately 2 cancers per 1000 screenees. There is suggestive evidence that the cancers discovered are more likely to be localized. For the present, physicians should limit colorectal cancer screening to persons at relatively high risk: persons aged over 45 years, with a family history of bowel cancer, or with polyps. Protocols should be designed to ensure high specificity. The recommendations of the National Cancer Institute's consensus conference provide practical guidelines pending the outcome of randomized controlled trials.