New research suggests that a screening technique in which doctors use instruments to view the colon and rectum may greatly reduce the risk of death from cancers that arise there.
But researchers found that the tests need be performed only every 10 years, rebutting arguments by some health organizations that patients should be tested every three to five years.
Although some experts raised cautions about the design of the study, reported in to day's New England Journal of Medicine, they also said it was one of the most comprehensive efforts to settle a long-standing controversy over the usefulness of the test, called sigmoidoscopy.
Another study of colorectal cancer, also reported in the journal yesterday, casts doubt on the widespread practice of considering everyone who has had benign growths, known as polyps, to be at high risk for colon or rectal cancer.
In this study, the researchers found that patients with large, irregular polyps were indeed at high risk; other patients were not.
In the sigmoidoscopy study, researchers from Kaiser Permanente Medical Care Program in Oakland, Calif., and the University of Washington found that testing, even as infrequently as every 10 years, can reduce a person's risk of death from these cancers by as much as 70 percent.
The principal author of the study, Dr. Joe Selby of Kaiser Permanente, added that further research might show it is possible to extend the time between tests beyond 10 years.
Health groups differ on their recommendations for screenings for colorectal cancer, which kills 60,000 Americans each year. The National Cancer Institute, the American Cancer Institute and the World Health Organization recommend testing every three to five years beginning at age 50.
But the Preventive Services Task Force, an arm of the Public Health Service, has argued that there is not enough evidence to justify screening people who do not have a high risk of cancer.
Sigmoidoscopy, which typically costs between $75 and $150, involves inserting a fiber-optic device called a sigmoidoscope into the rectum so that the examiner can look for abnormal growths or lesions inside the rectum and the lower part of the colon. Selby said more than half of all colorectal cancers are in the lower part of the colon.
Unlike breast, cervical, prostate and lung cancer, colorectal cancer begins with a harmless growth that doctors can easily see. These polyps allow colorectal cancer to be quickly detected and prevented.
Dr. Selby said most people should have their first test at age 50 and subsequent tests every 10 years. The researchers said it takes at least 10 years for a polyp to form, grow and become cancerous.
"It's possible that even longer than 10 years will suffice," said Dr. Selby. "If we could've looked longer we would've, but we just didn't have the data."
The recommendations of the study could have important implications for clinical practice because doctors tend to perform the procedure every three years.