Flexible sigmoidoscopy, a screening test for colorectal cancer that is less invasive and has fewer side effects than colonoscopy, is effective in reducing the rates of new cases and deaths from colorectal cancer, according to research sponsored by the National Cancer Institute, part of the National Institutes of Health.

In a study that spanned almost 20 years, researchers found overall colorectal cancer mortality was reduced by 26% and incidence by 21% as a result of screening with sigmoidoscopy, which has fewer side effects, requires less bowel preparation and poses a lower risk of bowel perforation than colonoscopy.

Colorectal cancer is the second-leading cause of cancer-related death in the United States, according to background information in the study, which appeared May 21 on the website of the New England Journal of Medicine and was scheduled for presentation at the Digestive Disease Week conference May 19-22 in San Diego.

Previous research showed that colorectal cancer incidence and mortality can be reduced with a number of screening methods, including fecal occult blood testing. However, flexible sigmoidoscopy and colonoscopy are more sensitive than FOBT for detecting polyps that may lead to colorectal cancer. Removal of precancerous polyps, which can be done during sigmoidoscopy or colonoscopy, reduces colorectal cancer risk.

“The most important message is that, regardless of modality chosen, colorectal cancer screening lowers mortality from colorectal cancer, and all individuals 50 and over should be screened,” study author Christine Berg, MD, chief of NCI’s Early Detection Research Group and project officer of the Prostate, Lung, Colorectal and Ovarian Cancer Screening (PLCO) Trial, said in a news release.

From 1993 to 2001, a total of 154,900 men and women ages 55 through 74 were randomly assigned to receive flexible sigmoidoscopy screening or usual care as part of the PLCO trial. People in the usual care group received screening only upon request or a recommendation from their physician. Participants assigned to the flexible sigmoidoscopy group were screened once on entering the study and again three years to five years later. The participants were followed for approximately 12 years to collect data on cancer diagnoses and deaths.

The researchers compared overall colorectal cancer mortality and incidence in the two groups, and also analyzed incidence and mortality according to the location of the cancers that developed. Cancers located from the rectum through a bend in the colon called the splenic flexure were defined as distal, and those in the transverse colon to the cecum were defined as proximal.

Although flexible sigmoidoscopy examines only the rectum and sigmoid colon, participants with a suspicious finding were referred for a follow-up colonoscopy, in which both the distal and proximal regions of the colon would be examined.

Overall, after an average of nearly 12 years, participants in the screening group had a 21% lower incidence of colorectal cancer overall and a 26% lower rate of colorectal cancer mortality than participants in the usual care group. At that rate, if 1,000 people followed the PLCO protocol of two sigmoidoscopy screenings over the course of 10 years, there would be approximately three fewer new cases and one fewer death from colorectal cancer than in a comparable group not receiving regular screenings.

The incidence of distal colorectal cancer was reduced by 29% and mortality from distal colorectal cancer by 50% in the screening group. Although there was no statistically significant decline in deaths from proximal colorectal cancer, the incidence of proximal colorectal cancer was reduced by 14% in the screening group.

“This is the second major trial that has shown that sigmoidoscopy is effective in reducing the risk of dying of colorectal cancer,” Barnett Kramer, MD, director of NCI’s Division of Cancer Prevention, said in the news release. “Sigmoidoscopy is less invasive than colonoscopy and carries a lower risk of the colon being perforated, which may make it more acceptable as a screening test to some patients.

“There are several effective screening tests for colorectal cancer, and the most effective screening test is the one that people choose to take.”

The researchers estimated that if they had used colonoscopy rather than sigmoidoscopy in this study, they would have identified 16% more cancers, two-thirds of which would have been proximal cancers. However, they were not able to determine what effect that finding may have had on proximal colorectal cancer mortality.

The authors said there has been some controversy about how effective colonoscopy is in decreasing colorectal cancer mortality in different regions of the colon, with some studies suggesting the screening is more effective against distal than proximal tumors. Sigmoidoscopy never has been directly compared to colonoscopy in a definitive clinical trial, they noted.

False-positive sigmoidoscopy results were observed in 20% of men and 13% of women in the screening group, but the researchers said some false positives could have been the result of false-negative colonoscopies done to follow up on suspicious sigmoidoscopy findings. Approximately 22% of people in the screening group were sent for follow-up colonoscopies during the screening phase of the trial.

To read the study, visit http://bit.ly/KsNcqq.