Colorectal cancer (CRC) is the second leading cause of cancer deaths in the United States. A screening test known as colonoscopy allows physicians to detect and remove precancerous polyps in the colon. Most guidelines recommend that men and women aged 50 and older have a colonoscopy every ten years. However, there is little scientific evidence to suggest whether ten years is the ideal interval between screening tests.

In an article published in the May 24/31, 2006 issue of the Journal of the American Medical Association (JAMA) , researchers report that people who have a negative colonoscopy (one in which no biopsy or removal of polyps is required) are 30-40% less likely than people in the general population to develop colorectal cancer over the next ten years. This suggests that once every ten years is often enough for a colonoscopy. A related article in the same JAMA issue suggests that in the very elderly, the costs and risks associated with colonoscopy may outweigh the benefits.

About the Study

The researchers examined the medical records of 35,975 men and women living in Manitoba, Canada who had had a negative colonoscopy between April 1989 and December 2003. They compared the incidence of colorectal cancer in this group to the incidence of colorectal cancer in the general population of Manitoba over the next ten years.

Compared to the general population, the negative colonoscopy group had a 31% lower incidence of CRC at six months; a 34% lower incidence at one year, a 41% lower incidence at two years, a 45% lower incidence at five years, and a 72% lower incidence at ten years.

How Does This Affect You?

This study demonstrated that men and women who have a colonoscopy that does not require a biopsy or polyp removal continue to have a significantly decreased risk for colorectal cancer ten years after undergoing the screening test. This, of course, only applies to individuals at average risk for CRC. Those with a strong family history or other known risk factors for this disease (eg, previous polyps or ulcerative colitis ) should continue to have colonoscopies done more frequently than every ten years.

In the related JAMA article, researchers compared the estimated increase in life expectancy from colonoscopy for the very elderly (aged 80 years and older) to younger patients (aged 50-54 years). They found that younger patients enjoy a 6.5-fold increase in life expectancy, compared to very elderly patients. Although the prevalence of precancerous colon polyps increases with age, the very elderly are more likely to die of other causes before these tumors develop into cancer.

These studies provide important insights for physicians and patients. Younger patients clearly benefit from relatively infrequent colonoscopies. As a result, physicians should educate their patients about colorectal cancer screening and encourage them to overcome any reservations they may have about the procedure.

On the other hand, for very elderly patients, the potential risks inherent in an invasive procedure such as colonoscopy, and the costs associated with it, may outweigh the benefits. Once you’ve reached 80, you and your doctor should examine your individual risks, concerns, and priorities to determine whether you should be screened.