Colonoscopy screening reduces risk of advanced colorectal cancer

A new study led by a researcher at the Perelman School of Medicine at the University of Pennsylvania adds support to current medical recommendations stating that screening colonoscopy substantially reduces an average-risk adult’s likelihood of being diagnosed with advanced colorectal cancer (CRC) in either the right or left side of the colon.

In recent years, colonoscopy has begun to rapidly replace sigmoidoscopy-a procedure used to detect abnormalities in the rectum and left side of the colon-despite initially limited evidence of its efficacy and higher cost.

In the new study, appearing online in the Annals of Internal Medicine, researchers noted an overall 70% reduction of advanced CRC diagnoses associated with receiving a screening colonoscopy. The results of the study suggest that colonoscopy has the ability to effectively identify tumors in both the left and right side of the colon before they progress to an advanced stage.

“Use of screening colonoscopy in average-risk adults was effective at reducing the risk of advanced colorectal cancer in both the right and left sides of the colon,” lead study author Chyke Doubeni, MD, MPH, presidential associate professor of Family Medicine and Community Health at Penn Medicine, told Formulary.

“We became interested in the study because of the rapid increase in the use of screening colonoscopy in the absence of direct evidence of its effectiveness coupled with studies showing that it may not be effective in the right side of the colon,” Dr Doubeni said. “The ability to reach the right side of the colon is a distinct advantage of colonoscopy over sigmoidoscopy, which can only examine the rectum and left colon.”

Previous research has established that screening with sigmoidoscopy or fecal occult blood test reduces the risk of death from CRC. By contrast, the efficacy of the colonoscopy-which examines the entire colon for precancerous and cancerous growths-in average-risk adults has remained largely uncertain. Colonoscopy’s effectiveness in the right colon (where approximately 50% of new CRC cases in the United States are found) has remained in doubt. 

In order to determine the efficacy of colonoscopy in preventing advanced colorectal cancer diagnoses, the researchers developed a case-control study in which data from four U.S. managed care organizations that participate in the HMO Cancer Research Network were evaluated. Medical records for 1,012 average-risk patients between aged 55 and 85 years were analyzed for the report. Among the 474 patients in the study who had advanced colorectal cancer, 251 of them (roughly 54%) had tumors in the right side of the colon-where sigmoidoscopy would not have been an effective screening modality. Randomized trials are currently underway to help researchers learn more about the effectiveness of colonoscopy, but those results will not be available for several years.

At Group Health, researchers found screening sigmoidoscopy was associated with a reduced risk of left-sided, but not right-sided, late-stage colorectal cancers.  “Cancers differ depending on whether they start on the left or right side of the bowel,” Dr Doubeni said.

“Colonoscopy is an effective screening test for reducing the risk of the more advanced lethal forms of colon cancers throughout the colon in average-risk adults over the age of 50,” he said.