One flexible sigmoidoscopy screening between the ages of 55 and 64 reduced both colorectal cancer diagnoses and deaths during a randomized clinical trial in the United Kingdom.
After following 170,000 people for more than 11 years, deaths from colorectal cancer were 43 percent lower among those who had a flexible sigmoidoscopy screening. Diagnosis of colorectal cancer was reduced by 33 percent.
This is the first prospective clinical trial that actually proved that examining the rectum and colon with a scope could reduce colorectal cancer deaths.
Participants in the trial had indicated their willingness to be part of a randomized trial and were assigned either to a control group or to receive a single flexible sigmoidoscopy exam. Twice as many people were in the control group as in the sigmoidoscopy group.
Participants were only people of average risk. Those with previous colorectal cancer, polyps, inflammatory bowel disease, or family history were not included.
Enrollment in the trial began in 1996 with a goal of following patients for 15 years.
During the a median 11 years of followup, there were 1,818 cases of colon or rectal cancer in the control group compared to 706 in the sigmoidoscopy group. Among those who didn’t have sigmoidoscopy, 538 people died of colorectal cancer and 189 died who did have the exam.
There was some selection bias — patients chose to enter the trial themselves but not whether they would get a sigmoidoscopy. After researchers adjusted for that bias, incidence of cancer was about a third less (33 percent) for those who got sigmoidoscopy and deaths were reduced by 43 percent.
In choosing sigmoidoscopy and age 55 to focus on screening, Dr. Wendy Atkins, who led the trial, pointed out that most people develop polyps in their 50′s and cancer later in life. About two-thirds of colon cancers are found in the distal colon, the part of the colon that can be reached by the sigmoidoscope.
The exams did not require sedation. Preparation was a single phosphate enema which participants administered at home about an hour before leaving for their appointment.
Dr. Atkins and her colleagues concluded,
Flexible sigmoidoscopy is a safe and practical test and, when offered only once between ages 55 and 64 years, confers a substantial and longlasting benefit.
In the United States, both the US Preventive Services Task Force and the American Cancer Society in collaboration with the Multi-Society Task Force on Colorectal Cancer and the American College of Radiology include flexible sigmoidoscopy in their colorectal cancer screening guidelines for people of average risk. For people with increased or high risk, only colonoscopy is recommended by both groups.
US guidelines call for flexible sigmoidoscopy to be done every five years.
In an earlier article in The Lancet that looked at patient acceptance, safety, and costs of the UK sigmoidoscopy screening trial, Dr. David Ransohoff, found that:
- 80 percent of patients experienced no more than mild pain during the test.
- Three months after the test, 98 percent were glad they had it and 97 percent would encourage a friend to have the exam.
- There was only 1 perforation in over 40,000 sigmoidoscopies, including 19,000 polyp removals.
- Among the 2,377 people referred for an additional colonoscopy, there were 4 perforations.
- 12 patients needed to be admitted to the hospital for bleeding after a sigmoidoscopy with polyp removal.
Costs concerns in the trial centered on the need for colonoscopy follow-up when a polyp is found in the distal colon to be sure no further polyps are located in the proximal colon out of the reach of the sigmoidoscope. In the UK trial only large adenomas were considered for colonoscopy follow-up. They were found in about 5 percent of cases. However, polyps of any size were discovered in 1 in 4 participants (25 percent) which, if followed by colonoscopy, would be more expensive.
Dr. Ransohoff suggests that it might be wise to tailor colorectal cancer screening strategies to individual risk. He writes,
Implementation of a tailored approach, by adjusting intensity of screening or surveillance to a person’s risk, requires consideration of three points: the individual’s absolute risk of colorectal cancer; the degree to which each screening or surveillance strategy reduces that risk; and quantitative definition of the goals of screening—ie, what level of absolute risk is high enough to justify the effort of reduction. By contrast, a one-size-fits-all approach to screening and surveillance may be easier to implement but less efficient. And in some cases—for example, when people with very low risk of subsequent colorectal cancer undergo potentially hazardous surveillance procedures such as colonoscopy—such an approach may even be harmful. A tailored approach, based on a quantitative definition of the goals of screening and surveillance, deserves increased consideration.
Ransohoff, The Lancet, Volume 359, Number 9314, April 2002
Interviews with Dr. Atkins and Jane Wardle, PhD from the trial and Dr. Jennifer Obel, speaking for the American Society of Clinical Oncology, done by MedPage Today are below: