Colorectal Cancer Screening and Prevention.

Colorectal cancer is a common cause of morbidity and mortality in the United States. Most colorectal cancers arise from preexisting adenomatous or serrated polyps. The incidence and mortality of colorectal cancer can be reduced with screening of average-risk adults 50 to 75 years of age. Randomized controlled trials show evidence of reduced colorectal cancer-specific mortality with guaiac-based fecal occult blood tests and flexible sigmoidoscopy. There are no randomized controlled trials on the effectiveness of colonoscopy to reduce colorectal cancer-specific mortality; however, several randomized controlled trials comparing colonoscopy with other strategies are in progress. The best available evidence supporting colonoscopy is from prospective cohort studies that demonstrate decreased incidence of colorectal cancer and colorectal cancer-related mortality in individuals undergoing colonoscopy. Other screening options include fecal immunochemical testing, computed tomographic colonography, and multitargeted stool DNA testing combined with fecal immunochemical testing. There is good evidence that aspirin, nonsteroidal anti-inflammatory drugs, cyclooxygenase-2 inhibitors, and hormone therapy decrease the risk of colorectal cancer and adenomatous polyps, but potential harms limit their usefulness. There is good evidence that calcium supplementation, moderate dairy consumption, reduced red meat consumption, increased physical activity, decreased body mass index, and statin use decrease the risk of colorectal cancer and adenomatous polyps. Although increased alcohol intake and tobacco use are associated with an increased risk of colorectal cancer, there is no direct evidence that reducing alcohol consumption or smoking cessation decreases the risk.