To screen or not to screen for colon cancer…. Most doctors advise their patients to begin colonoscopies starting at age 45. A recent study investigated this highly recommended screening with disappointing results.
Colonoscopy is the most commonly used screening exam for colon cancer. During this test, a flexible scope is inserted into the rectum and the whole colon is explored. For people at normal risk for colon cancer, colonoscopies usually start at about age 45 and are continued every 10 years through age 75.
Not Much Difference Between Screened and Unscreened
A new study from Europe that compared colonoscopy-screened people to unscreened people found that colonoscopies lowered the risk of colon cancer…but at a disappointing rate. And the screening did not significantly lower the risk of death from colon cancer. The study is from the Northern-European Initiative on Colon Cancer. In this trial, people in Northern Europe were invited to have a colonoscopy screening. After 10 years, these people were compared to a larger group of people who had no screening.
The trial included 84,585 healthy men and women, ages 55 to 64. These people came from Poland, Norway, Sweden and the Netherlands. Colonoscopy screening was done between 2009 and 2014. Colon cancer risk and deaths related to colon cancer were recorded at 10 years after colonoscopy. The results are published in The New England Journal of Medicine. These were the key results…
- For people who were screened with colonoscopy, the risk of a colon cancer diagnosis was about one percent.
- For people not screened, the risk of colon cancer diagnosis was 1.2 percent, meaning the risk for these people was 18 percent higher.
- The risk of death from colon cancer in the screened group was 0.28 percent.
- The risk of death from colon cancer in the unscreened group was 0.31 percent. The researchers interpreted this as not a significant difference.
- The researchers found that they would need to do 455 colonoscopies to prevent one colon cancer.
Colonoscopy may prevent colon cancer by removing colon growths called polyps that have the potential to turn cancerous in the future. Although the study did find some prevented cancers, the rate of prevention and the failure to show a significant decrease in deaths due to colon cancer were less than expected and described as disappointing.
Reasons for Fewer-Than-Expected Saved Lives
One factor that may have contributed to the disappointing results was the low rate of people who accepted the invitation to colonoscopy. The rate of acceptance was only 42 percent. More colonoscopies may have improved the rate of prevention. The researchers projected that if all the people invited had been screened with colonoscopy, it could have reduced colon cancer diagnosis by 31 percent, but even this number is lower than expected.
Another reason the study did not show a reduction in colon cancer death was that it only followed up for 10 years. Colon cancers may take 15 years to develop.
Colonoscopy Is Not the Only Way to Find Cancer
One interpretation of the study is that colonoscopy may not be substantially better than other screening techniques. According to the CDC and the U.S. Preventive Services Task Force guidelines, there are several options for colon cancer screening…
- Stool tests that look for blood, cancer DNA, and cancer antibodies can be done once every three years.
- Flexible sigmoidoscopy, which is similar to colonoscopy but limits the exam to the rectum and lower colon, can be done every five years.
- Virtual colonoscopy, which is an imaging study of the colon displayed on a computer screen, can be done every five years.
- Colonoscopy, which has the advantage of examining the entire colon and removing a polyp or early cancer in a polyp, can be done every 10 years.