Research conducted at the University of Alabama at Birmingham as part of a national study reveals that flexible sigmoidoscopy — a screening test for colorectal cancer that is less invasive and has fewer side-effects than colonoscopy — reduces deaths due to colorectal cancer.
Overall, colorectal cancer deaths were reduced 26 percent and new cases were reduced 21 percent as a result of screening with sigmoidoscopy, according to findings of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial that appeared online May 21, 2012, in the New England Journal of Medicine.
As part of the PLCO trial, a population-based, randomized study funded by the National Cancer Institute, a total 154,900 men and women ages 55-74 were randomly assigned to receive flexible sigmoidoscopy screening (intervention group) or usual care (control group) between 1993 and 2001. Control group participants were screened only if they asked for it or if their physician recommended it. Members of the intervention group were screened upon entering the study to collect a baseline measure and again three to five years later. All participants were followed for approximately 12 years.
UAB enrolled more than 6,000 participants. Compliance was one of the highest among all 10 sites — 96 percent at baseline and 75 percent at five years.
"This trial allowed us to identify an evidence-based screening tool other than colonoscopy to reduce the number of new cases and deaths from colorectal cancer. This finding is important because not all individuals have access to colonoscopy, which is more expensive and has to be performed by specialty physicians," says Mona Fouad, M.D., M.PH., principal investigator of the UAB PLCO site, director of the UAB Division of Preventive Medicine and co-leader of the Cancer Control and Populations Sciences program at the UAB Comprehensive Cancer Center.
Sigmoidoscopy involves examination of the lower colon using a thin, flexible tube-like instrument, called a sigmoidoscope, to view the anus, rectum and sigmoid colon. It has fewer side-effects, requires less bowel preparation, does not require sedation and poses a lower risk of bowel perforation than colonoscopy, in which a similarly flexible but longer tube is used to view the entire colon.
Colorectal cancer is the second-leading cause of cancer-related deaths in the United States. Previous research has shown that its 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 pre-cancerous polyps, which may be removed during the procedure to reduce the risk of colorectal cancer.
"The most effective screening test for colorectal cancer is the one people are willing to take. The results of this study may encourage more people to have colorectal screening with the less invasive and less expensive sigmoidoscopy," says Fouad.
In the PLCO trial, researchers compared the overall colorectal cancer mortality and incidence in the two groups (intervention and control) and also analyzed incidence and mortality according to the location of the cancers that developed. Cancers located in the area from the rectum through a bend in the colon called the splenic flexure were defined as distal, and those located in the transverse colon to the cecum were defined as proximal. Although flexible sigmoidoscopy examines only the rectum and the sigmoid colon, participants with a suspicious finding were referred for a follow-up colonoscopy, in which both the distal and the proximal regions of the colon were examined.
After an average 12 years, participants in the screening group had a 21 percent lower incidence of colorectal cancer and a 26 percent lower mortality rate than participants in the usual-care group. The incidence of distal colorectal cancer in the screening group was reduced 29 percent, and mortality from distal colorectal cancer was reduced 50 percent. While there was no statistically significant decline in deaths from proximal colorectal cancer in the screening group, the incidence of proximal colorectal cancer was reduced 14 percent.
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