Colonoscopy appears to reduce the risk of developing or dying from colorectal cancer more substantially than does sigmoidoscopy, according to data from the Nurses Health Study and Health Professionals Follow-up Study.
The investigation, published in the Sept. 19 issue of the New England Journal of Medicine, also identifies molecular features that may help explain tumors that are diagnosed in individuals who recently have undergone colonoscopy.
This study provides some of the clearest evidence to date that colonoscopy has advantages over sigmoidoscopy for the prevention of colon cancer, although it is not a perfect test, Andrew Chan, MD, MPH, who works in the Massachusetts General Hospital Gastrointestinal Unit and is a senior author of the report, said in a news release.
Our findings support current recommendations for colorectal cancer screening with either of these procedures and provide a rationale for some individuals to consider colonoscopy as a preferred test for their individual situation.
Both colonoscopy and sigmoidoscopy allow examination of the internal surface of the colon through a fiberoptic tube with a light and camera at the end, but while colonoscopy visualizes the entire colon, sigmoidoscopy reaches only the lower third on the left side of the body. Recommendations for colorectal screening in average-risk individuals over age 50 are either a sigmoidoscopy every five years followed by colonoscopy if abnormalities are detected or a colonoscopy every 10 years.
While randomized, controlled clinical trials have confirmed that sigmoidoscopy reduces the incidence of and death from colorectal cancer, similar trials have not been done for colonoscopy, and some prior studies have suggested that colonoscopy did not have significant advantages over sigmoidoscopy. However, the more comprehensive colonoscopy is widely recommended for colorectal screening based on its ability to visualize the whole colon.
Methodology and results
The new study was designed to compare the effectiveness of both procedures in reducing the long-term risk of colorectal cancers in different segments of the colon and to examine molecular features of tumors developing soon after a negative examination.
The investigators analyzed information from almost 89,000 participants in the Nurses Health Study and the Health Professionals Follow-up Study, both of which gather comprehensive health information from their participants every two years. From 1988 to 2008, the participants reported whether they had either sigmoidoscopy or colonoscopy in the two preceding years and, if so, whether the examinations were for screening purposes or because of symptoms such as bleeding. For participants who developed cancer or who reported having colon polyps removed, the researchers obtained consent to review their medical records and pathology reports.
Over the 22 years for which data was analyzed, 1,815 cases of colorectal cancer and 474 related deaths were documented in the 88,902 study participants. While a negative result in either examination or having polyps removed was associated with a reduced risk of developing left-side colon cancer, only a negative colonoscopy was associated with significant risk reduction in the entire colon.
Compared with the 15% of study participants who had no endoscopic colon exam during the study period, having either procedure significantly reduced the overall risk of dying from colorectal cancer. But while sigmoidoscopy cut the risk of dying only from left-side tumors, colonoscopy reduced the risk of any colorectal cancer-associated death.
Having a single negative colonoscopy significantly reduced the incidence of any colorectal cancer for up to 15 subsequent years, supporting the current recommendations for a 10-year interval between exams. Among participants who had polyps removed, the incidence of subsequent tumors was reduced for up to five years, except for those whose polyps had features indicating elevated risk, in whom the risk reduction was not as strong.
For individual patients, the decision to select colonoscopy over sigmoidoscopy for colorectal cancer screening requires discussing with their physicians how the advantages and disadvantages of each test apply to their personal situations, Chan said. Right now our data support the use of colonoscopy if the primary goal is maximum risk reduction for both left- and right-side colorectal cancers.
Future study should focus on ways of further improving colonoscopy quality, as well as better understanding why some tumors arise within a short time after a negative examination.
Among the participants who developed colorectal cancer, molecular data was available on 62 tumors that had been diagnosed within five years after colonoscopy. The researchers identified specific cancer-related features more likely to be seen in those tumors than in cancers diagnosed after more time had passed.
It is widely believed that tumors with those features develop from a specific type of polyp called a sessile serrated adenoma, which may be particularly difficult to detect endoscopically or to remove completely, Chan said. Focused efforts to improve detection and removal of these polyps are a high priority.”
Study abstract: http://www.nejm.org/doi/full/10.1056/NEJMoa1301969.