August 28, 2014
News Review From Harvard Medical School -- Polyp Removal and Future Colon-Cancer Risk
People who have low-risk colon polyps removed may have a lower-than-average risk of future colon cancer, a new study suggests. But those who have high-risk polyps removed may still have a higher risk. The study was done in Norway. It was based on data for nearly 41,000 people. They had colorectal polyps called adenomas removed during a colonoscopy. This test uses an instrument to look inside the colon for cancer. Adenomas are removed because they sometimes become cancerous. The study group was divided into low-risk and high-risk groups. The low-risk group had a single polyp smaller than 1 centimeter removed. During about 8 years of follow-up, people in this group were 25% less likely to die of colon cancer than someone in the general population. People in the high-risk group had large or multiple polyps removed. During the follow-up period, their risk of colon-cancer death was 16% higher than that of the general population. Under current U.S. guidelines, those in the low-risk group would receive more frequent colonoscopies. The study results suggest that this is not needed, a study author told HealthDay News. The New England Journal of Medicine published the study August 28.
By Robert H. Shmerling, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Colon cancer is a leading cause of death among adults in the United States. Fortunately, we have good screening tests with the potential to save lives. Colonoscopy is the best screening test for colon cancer.
During a colonoscopy, a doctor peers into the colon through a flexible tube with a light and camera on the tip. If a tumor is seen, a sample (biopsy) can be removed to find out whether it is cancerous. A small tumor can be removed during the procedure.
Colonoscopy can prevent deaths due to colon cancer by:
- Detecting cancer at a curable stage
- Detecting (and removing) certain types of polyps called adenomas, which sometimes become cancerous
- Leading to more frequent testing in the future if cancer or some kinds of polyps are found
How much of the benefit of colonoscopy is due to detection of polyps? That's the subject of a study just published in the New England Journal of Medicine.
Researchers in Norway did the study. They used the nationwide health monitoring system to identify who had a polyp removed and later developed colon cancer or died.
They looked at data on nearly 41,000 people who had polyps removed. During an average follow-up of 8 years:
- 1,273 developed colorectal cancer and 383 died of the disease.
- People who had low-risk polyps removed were 25% less likely to die of colorectal cancer than the expected rate in the general population. A low-risk polyp was defined in this study as an adenoma that was single, small or lacked certain features when viewed under a microscope.
- People who had high-risk polyps removed were about 16% more likely to die of colorectal cancer than the expected rate for the general population.
This last finding could be interpreted as a failure of colonoscopy. People with high-risk polyps still had a higher than expected rate of colon-cancer death even though polyps were removed.
However, I think this would not be a correct interpretation. Here's why:
- The average follow-up in the study was only eight years. It may take longer to show the protective effect of polyp removal.
- At the time of this study, the guidelines in Norway recommended less frequent screening after polyp detection than current guidelines. More frequent screening could have produced better results.
- The rate of colorectal cancer-related deaths might have been even higher in those with high-risk polyps if they had not had colonoscopies.
- Removal of the low-risk polyps was linked with a reduction in colorectal cancer-related deaths. That's probably because removing the tumors alone lowers risk.
- This study involved people with symptoms, such as bleeding. Results could have been different if the polyps had been discovered by routine screening.
- In this study, some polyps may have been missed or incompletely removed. The solution for this is better colonoscopies, not fewer of them.
A wealth of data links screening colonoscopy with a decrease in deaths related to colorectal cancer. This study should not discourage anyone from having a screening colonoscopy.
What Changes Can I Make Now?
You can reduce your risk of colon cancer and increase the chance of detecting the disease at a curable stage. Here's what you can do:
- Eat a diet that is high in fiber, vegetables and folate while avoiding saturated fat, processed meat and excessive alcohol or calories.
- Exercise each day.
- Take a daily, low-dose aspirin (but talk to your doctor first).
- Have colonoscopies (and/or other screening) as recommended.
Current guidelines recommend a colonoscopy every 10 years for people at average risk of colon cancer. Screening should begin at age 50 and end at age 75 to 85. Earlier and more frequent screening may be recommended for some people, such as those with a history of colon cancer or a strong family history of the disease.
Other screening options include:
• Rectal examinations
• Testing of the stool for blood
• Sigmoidoscopy (an internal examination of the last part of the colon)
• Barium enema
• CT scanning
However, these are less effective. Don't rely on these as your only means of screening. If you have had colon cancer or an adenoma in the past, talk to your doctor about how often to have follow-up screening.
What Can I Expect Looking to the Future?
You can expect more studies of colonoscopy among people at average or high risk of colorectal cancer. We may discover how often to repeat screening for those at increased risk and also who can safely skip screening.
For those with adenomas, the ideal study would randomly assign people to have a repeat colonoscopy at various time intervals over a decade or more. Until such studies are completed, I think it's best to follow current guidelines.