NIH study finds sigmoidoscopy reduces colorectal cancer rates

May 24, 2012 10:18 am Dr K K Health Care

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 due to 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 that overall colorectal cancer mortality (deaths) was reduced by 26% and incidence (new cases) was reduced by 21% as a result of screening with sigmoidoscopy. These results appeared online on May 21, 2012, in the New England Journal of Medicine.

Sigmoidoscopy involves examination of the lower colon using a thin, flexible sigmoidoscope, to view the anus, rectum, and sigmoid colon. It has fewer side effects, requires less bowel preparation and poses a lower risk of bowel perforation than colonoscopy.

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.

From 1993 to 2001, a total of 154,900 men and women aged 55 through 74 were randomly assigned to receive flexible sigmoidoscopy screening or usual care as part of the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening trial. People in the usual care group (i.e. control group) only received screening if they asked for it, or if their physician recommended it. This large population-based randomized trial was designed to determine the effects of screening on cancer-related mortality. Participants assigned to the flexible sigmoidoscopy group were screened once on entering the study (baseline) and again three years to five years later. The participants were followed for approximately 12 years to collect data on cancer diagnoses and deaths.

? 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. This means that, over the course of 10 years, if 1,000 people followed the PLCO protocol of two sigmoidoscopy screenings, 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 was reduced by 50%, in the screening group.
? While 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. 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,? said Barnett Kramer, M.D., director of NCI?s Division of Cancer Prevention. ?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 may have had on proximal colorectal cancer mortality. 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 that it is more effective against distal than proximal tumors. Sigmoidoscopy has never been directly compared to colonoscopy in a definitive clinical trial.

False-positive sigmoidoscopy results were observed in 20% of men and 13% of women in the screening group, but some of these 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. [Source NIH]

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