A new study adds support to current medical recommendations stating that screening colonoscopy substantially reduced the likelihood of advanced colorectal cancer (CRC) in either the right or left side of the colon being diagnosed in an average-risk adult. Undergoing screening colonoscopy was associated with 70% fewer diagnoses overall of advanced CRC. This study suggests 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.

In recent years, colonoscopy has begun to rapidly replace sigmoidoscopy, which is used to detect abnormalities in the rectum and left side of the colon, despite the initially limited evidence of efficacy and higher cost of colonoscopy. Although the incidence of CRC and cancer-related deaths is decreasing, CRC remains the third most common cancer worldwide and the second leading cause of cancer deaths. Experts say that given what is known about the efficacy of screening colonoscopy, the procedure is underutilized.

“Colorectal cancer is one of the most important cancers we face in this country. It was responsible for over 50,000 deaths in 2012, and the truth is, most of those deaths are preventable through screening, early detection, and treatment,” said lead author Chyke Doubeni, MD, MPH, of Perelman School of Medicine at the University of Pennsylvania in Philadelphia. “Our goal with this study was to understand the extent to which colonoscopy can prevent the diagnosis of advanced colorectal cancers, the ones that primarily result in death. What we saw was a dramatically reduced risk of death for patients who were screened.”

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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 US managed care organizations that participate in the HMO Cancer Research Network were evaluated. Medical records for 1,012 average-risk patients between 55 and 85 years old were analyzed for the report. Among the 474 patients in the study who had advanced colorectal cancer, 251 of them (approximately 54%) had tumors in the right side of the colon, which is where sigmoidoscopy would not have been an effective screening modality. Randomized trials are currently under way to help researchers learn more about the effectiveness of colonoscopy, but those results will not be available for several years.

This study confirms the effectiveness of screening colonoscopy and reinforces its importance for all adults older than 50 years. “As we wait to learn more about the effectiveness of screening colonoscopy through clinical trials, this case-control study provides credible answers that support current screening practices and recommendations,” said Robert H. Fletcher, MD, MSc, professor emeritus at Harvard Medical School and co-author on the study.

This study was published in Annals of Internal Medicine (2013;158[5Part1]:312-320).