According to a large, long-term study from Harvard School of Public Health, 40 percent of all colorectal cancers might be prevented if people underwent regular colonoscopy screening. The new research also supports existing guidelines that recommend that people with an average risk of colorectal cancer should have a colonoscopy every 10 years. The new study helps address previous uncertainty about the effectiveness of colonoscopy in reducing colorectal cancer incidence and mortality – particularly among people with cancer that originates in the proximal, or upper part of the colon. The study appears in the September 19, 2013 edition of the New England Journal of Medicine.