CHICAGO – Among older patients, the rate of new or missed left-sided colorectal cancers quadrupled with flexible sigmoidoscopy compared with colonoscopy in a retrospective analysis of 25,541 cases.
The overall interval colorectal cancer (CRC) rate, defined as colorectal cancer diagnosed 6-36 months after a lower endoscopy, was 11.7% after flexible sigmoidoscopy vs. 2.6% after colonoscopy, Dr. Yize Richard Wang reported in a late-breaking abstract session at the annual Digestive Disease Week.
The rate of interval CRCs was higher after sigmoidoscopy than colonoscopy in all locations: the descending colon (18.7% vs. 3.3%), rectum (12.5% vs. 2.7%), left colon combined (11.7% vs. 2.6%), sigmoid colon (11.3% vs. 2.4%) and rectosigmoid junction (8% vs. 2.2%).
"Despite the imperfections of colonoscopy, it remains the gold standard for colorectal cancer detection and prevention," concluded Dr. Wang, a fellow with the Mayo Clinic in Jacksonville, Fla.
Dr. Yize Richard Wang
Although some news reports hailed the study as a boon for colonoscopy, it is unlikely to resolve the long-standing debate over which screening method is optimal. Sigmoidoscopy requires no sedation and less time and bowel preparation for the patient, but cannot visualize the entire colon. Colonoscopy typically requires sedation and has a higher perforation rate, but allows for examination of the entire colon and removal of any detected polyps. Still, these benefits have not translated into an unequivocal reduction in the incidence and mortality from cancer beyond the reach of sigmoidoscopy.
A recent commentary on colonoscopy vs. sigmoidoscopy screening (JAMA 2010;304:461-2) states that if "further evidence supports a lack of efficacy of colonoscopy for reducing incidence and mortality for right-sided colorectal cancer, the medical community should be prepared to consider returning to sigmoidoscopy for endoscopic screening of average-risk individuals."
Just 2 years ago at the same meeting, researchers with the Norwegian Colorectal Cancer Prevention Centre reported that the use of flexible sigmoidoscopy among 55,736 patients aged 55-64 years reduced colorectal cancer mortality 27% after 6 years, compared with no screening. The trend was not statistically significant, but when the researchers limited the analysis to patients who were randomized and actually underwent flexible sigmoidoscopy, there was a significant 59% reduction in total colorectal cancer mortality and significant 76% reduction in rectosigmoid cancer (BMJ 2009 May 29;338:b1846 [doi:10.1136/bmj.b1846]).
The current study included 25,541 patients 67 years and older at the time of a lower endoscopy during 1988-2005, who were subsequently diagnosed within 36 months with CRC distal to the splenic flexure. All but 841 of the 25,541 cases were detected within the first 6 months.
The patients were identified in the Surveillance, Epidemiology, and End Results–Medicare linked database. Exclusion criteria included participation in an HMO, no Medicare Part B coverage for the 24 months preceding the exam, inflammatory bowel disease, and a history of polyps or family history of colorectal cancer.
Compared with the colonoscopy group, the flexible sigmoidoscopy group was slightly older (78 vs. 77 years), included more women (53% vs. 50%) and fewer nonwhites (14% vs. 16%), lived in ZIP codes with higher income/education (no data given), and were more likely to be seen by nongastroenterologists (66% vs. 33%), Dr. Wang said.
In multivariate logistic analysis, women were at 15% higher risk of interval CRC (odds ratio 1.15), while undergoing an inpatient procedure reduced the risk by 47% (OR 0.53).
The odds ratio for an interval CRC with flexible sigmoidoscopy was 4.0 (95% confidence interval 3.51-4.55).
During a discussion of the study, attendees asked whether detection rates were different among gastroenterologists and nongastroenterologists. Dr. Wang replied that there was no difference (OR 1.09 for nongastroenterologists), but that a difference was observed in the right-side colon in another study presented at the meeting.
Dr. Wang pointed out that the retrospective study had several limitations including the inability to determine the indication for, or findings of, the lower endoscopy. It also does not apply to patients undergoing screening colonoscopy for detection and removal of polyps, and does not reflect recent advances in endoscopy such as high-definition colonoscopy.
"Whether our findings reflect differences in bowel preparation quality, lack of sedation, or depth reached during sigmoidoscopy, warrants future research," he said.
Two independent randomized trials of screening colonoscopy are ongoing (NCT00906997 and NCT00883792), but results are not expected until 2021 and 2026.
Dr. Wang disclosed no relevant conflicts of interest.