Researchers at the Harvard School of Public Health (HSPH) in Boston, Massachusetts, found that 40% of all colorectal cancers could be prevented if people underwent regular colonoscopy screening. Their results, from a large long-term study, support current guidelines that recommend people of average risk for the disease undergo colonoscopy every 10 years.
Co-senior author Shuji Ogino, MD, PhD, an associate professor in the department of epidemiology at HSPH, says that previously insufficient evidence existed regarding how much colonoscopy reduces colorectal cancer incidence and mortality, particularly among patients in whom the cancer originates in the proximal part of the colon. Evidence from this study demonstrates that colonoscopy is effective in preventing cancer in both the distal and proximal regions of the colorectum, whereas sigmoidoscopy alone is insufficient for preventing proximal disease, he adds.
Dr. Ogino and his colleagues reviewed data from 88,902 participants in both the Nurses' Health Study and Health Professionals Follow-Up Study. Participants completed questionnaires every 2 years between 1998 and 2008, and researchers documented 1815 cases of colorectal cancer and 474 deaths from the disease. They found that colonoscopy and sigmoidoscopy were linked to a decreased risk of either developing colorectal cancer or dying of it.
Although colonoscopy was found to lessen the risk of cancers originating in the proximal colon, it was more effective against those arising in the distal colon. The procedure's decreased effectiveness in reducing the risk of tumors developing in the proximal colon may be attributed to molecular and biological differences between the 2 cancers, researchers say.
Additional findings include:
- If all study participants had undergone colonoscopies, an estimated 40% of colorectal cancers, would have been prevented.
- Individuals who undergo colonoscopies and are cleared of any problems have a significantly reduced risk of colorectal cancer for up to 15 years after the procedure; however, those with a personal history of adenoma or a family history of colorectal cancer should be screened more often.
- Colorectal cancers diagnosed within 5 years of a colonoscopy had different molecular characteristics compared with those diagnosed more than 5 years after the procedure. They also may be harder to detect and fully remove.