Even in patients whose last negative colonoscopy was more than 10 years before, advanced adenomas were rare, Dr. Hermann Brenner and colleagues reported.
The finding suggests that “extension of screening intervals, which could strongly enhance acceptance and cost-effectiveness of endoscopy-based screening and reduce its discomfort, might be achieved while maintaining high levels of safety,” they wrote (Gastroenterology [doi:10.1053/j.gastro.2009.10.054]).
A previous case-control study, also led by Dr. Brenner of the division of clinical epidemiology and aging research at the German Cancer Research Center in Heidelberg, Germany, found a significant 67% reduction in risk for colorectal cancer among people who had a negative colonoscopy between 10 and 19 years prior, and a nonsignificant reduction in risk among people whose negative screening was 20 or more years before (Gut 2006;55:1145-50).
However, that study had been restricted to colorectal cancer only and had not looked at adenoma rates.
“The current study provides evidence that a similarly very low risk is also seen if advanced colorectal adenomas are included in a combined end point of advanced neoplasms,” wrote the authors. “Taken together, these patterns support suggestions that a very low risk of clinically relevant colorectal neoplasms prevails far beyond 5 or 10 years after a negative colonoscopy, the most commonly recommended intervals for endoscopic screening examinations of the large bowel.”
In the current study, Dr. Brenner and his colleagues looked at 2,701 patients who had never had a colonoscopy, as well as 533 patients who had a history of one or more prior negative colonoscopies (and no prior positive colonoscopy). “Three-quarters of participants with previous negative colonoscopies had just one previous colonoscopy, almost 20% had two previous colonoscopies, and only 5% had three or more previous colonoscopies,” wrote the authors.
All patients completed a questionnaire that asked about colonoscopy history, and then they underwent colonoscopy.
All of the participants were age 55 years or older. In the colonoscopy-naive group, the mean age was 63.8 years and about half of the participants were female. In the group of patients who had a history of negative colonoscopy, there was a slightly greater proportion of women (57.6%) and the mean age was slightly older (65.1 years). The mean time since last colonoscopy was 11.9 years.
Patients were excluded from the study if they had a history of inflammatory bowel disease or a preceding colonoscopy within the same year as the study.
“Among participants without previous colonoscopy, the most advanced finding at screening colonoscopy was colorectal cancer in 41 cases (1.5%), advanced adenoma in 267 cases (9.9%), and other adenoma in 494 cases (18.3%),” they wrote.
In patients with a previous negative colonoscopy, no patients had colorectal cancer, and 25 (4.7%) had advanced neoplasm.
“These numbers are far and significantly below the numbers that would have been expected based on the age- and sex-specific prevalences in participants undergoing first-time colonoscopy,” wrote the authors—8.4 cases for colorectal cancer and 59.4 for advanced neoplasm, in a cohort of this size.
Additionally, “among those with a negative colonoscopy more than 15 years ago, the prevalence was still more than 40% lower than among those with no previous colonoscopy, even though this difference failed to reach statistical significance,” they added.
The authors conceded that one weakness of the study was that data regarding prior colonoscopy and results were self-reported; however, “in about 95% of self-reported negative colonoscopies, lack of polypectomy was confirmed by medical records,” they added.
The authors reported no conflicts of interest related to this study, which was supported only by a grant from the Central Research Institute of Ambulatory Health Care in Germany, Berlin.