The prevalence of left-sided advanced colorectal neoplasms was lower in participants in a community setting, but not right-sided advanced neoplasms, who had received a colonoscopy in the preceding 10 years, according to a new study published online December 30 in the Journal of the National Cancer Institute.

Effectiveness of colonoscopy in preventing colorectal cancer has been studied, but evidence from community settings is sparse, especially with respect to anatomical site.

To study this, Hermann Brenner, M.D., MPH, of the Division of Clinical Epidemiology and Aging Research, German Cancer Research Center, in Heidelberg, Germany, and colleagues conducted a cross-sectional study among 3,287 participants of screening colonoscopy aged 55 years or older from the state of Saarland between May 2005 and December 2007. Previous colonoscopy history was obtained by standardized questionnaire, and its association with prevalence of advanced colorectal neoplasms was estimated.

Advanced colorectal neoplasms were detected in 308 (11.4%) of the 2,701 participants with no previous colonoscopy compared with 36 (6.1%) of the 586 participants who had undergone colonoscopy within the preceding 10 years. Prevalence of left-sided advanced colorectal neoplasms, but not right-sided advanced neoplasms, was substantially lower within a 10-year period after colonoscopy in this community setting.

"Although a strong protective effect of colonoscopy from colorectal neoplasms has been established through previous studies, our results add to the evidence that this effect is much stronger in, if not confined to, the left colon and rectum, at least in the community setting," the authors write.

In an accompanying editorial, Nancy N. Baxter, M.D., Ph.D., of the Division of General Surgery at St Michael's Hospital, University of Toronto, and Linda Rabeneck, M.D., MPH, of the Department of Health Policy, Management, and Evaluation at the University of Toronto and Odette Cancer Centre, Sunnybrook Health Sciences Centre Toronto, note that these results are an important contribution to the growing body of literature of colonoscopy effectiveness research but still leave questions about the incremental benefits of screening colonoscopy. The editorialists point to some of the limitations of the literature.

"Simply put, is the effectiveness of colonoscopy 'good enough' for population-based screening?" they write. "As more observational evidence accumulates, the answer to this question becomes less certain."