News Summary

The first randomized U.S. trial of flexible sigmoidoscopy screening has found the tool is useful in screening for colorectal cancer, is effective in reducing the rates of fatal colorectal cancer cases and is less invasive with fewer side effects than colonoscopy.

To arrive at their results, researchers from 10 institutions worked for nearly two decades to track the health of more than 154,000 patients.

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The first randomized U.S. trial of flexible sigmoidoscopy screening has found the tool is useful in screening for colorectal cancer, is effective in reducing the rates of fatal colorectal cancer cases and is less invasive with fewer side effects than colonoscopy. The test can also detect precancerous issues early, leading to a decline in rates of new colorectal cancer cases.

The Prostate Lung Colorectal and Ovarian (PLCO) cancer screening trial, which ran from 1993 to 2000, included 154,900 men and women ages 55 through 74. Of the trial’s 10 testing sites, nearly 29,000 participants were enrolled by the University of Minnesota.

At the conclusion of the trial, researchers found that as a result of sigmoidoscopy screening, colorectal cancer deaths were reduced by 26 percent and new colorectal cancer cases declined 21 percent among trial participants as a result of earlier detection of precancerous polyps.

The results of the trial appear online today in the New England Journal of Medicine, and were presented at the scientific conference Digestive Disease Week.

“Colorectal cancer is the second-leading cause of cancer-related death in the United States, but the prospect of receiving a colonoscopy can scare some patients into avoiding screening altogether,” said School of Public Health professor Timothy Church, Ph.D., a cancer prevention expert and the University’s principle investigator on the trial. “Previous research here at the University of Minnesota demonstrated that screening reduced the number of fatal colorectal cancer cases, and now this study shows we can offer flexible sigmoidoscopy as a viable screening method.”

According to Church, of all the screening options, flexible sigmoidoscopy and colonoscopy are the most sensitive for detecting polyps that may lead to colorectal cancer. Removal of pre-cancerous polyps – which can be done during sigmoidoscopy or colonoscopy – reduces colorectal cancer risk.

A sigmoidoscopy, however, examines the lower colon using a thin, flexible tube-like instrument. The procedure has fewer side effects, requires less bowel preparation and poses a lower risk of bowel perforation than colonoscopy, which uses a similar but longer tube to view the entire colon.

Results more than a decade in the making

To arrive at their results, researchers from 10 institutions worked for nearly two decades to track the health of more than 154,000 patients.

“The University of Minnesota saw almost a fifth of the trial participants,” said Dr. Church. “We worked closely with the nine other institutes to help promote and enroll patients within the other communities across the country.”

Participants in the trial were randomly assigned to a flexible sigmoidoscopy screening group or a usual care group that only received screening if they asked for it or when their physician recommended it. The flexible sigmoidoscopy group participants were screened once when they entered the study and again three to five years later.

The researchers compared overall colorectal cancer cases and deaths in the two groups, and analyzed incidence and mortality according to where the cancers developed.

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.

At the end of the 12 year trial, participants in the screening group had a 21 percent lower incidence of colorectal cancer overall as a result of catching precancerous trouble spots earlier and a 26 percent lower rate of colorectal cancer mortality than participants in the usual care group.

The findings showed that over the course of 10 years, if 1,000 people had two sigmoidoscopy screenings, there would be approximately three fewer new cases and one less death from colorectal cancer than in a group the same size not receiving regular screenings.

“The most important screening is the screening that happens,” said Church. “If patients are more comfortable knowing they can drive home after a screening or want a less invasive screening, the latest research shows sigmoidoscopy may be the answer.”