Original article—alimentary tractColorectal Cancers Detected After Colonoscopy Frequently Result From Missed Lesions
Section snippets
Study Population
For the base-case analysis we analyzed a hypothetical cohort of 1000 average-risk adults undergoing a screening colonoscopy. In a secondary analysis we evaluated the risk of 1000 individuals who had at least one adenoma at a screening colonoscopy. We developed a mathematical model using Excel (Microsoft Office 2008; Microsoft Corporation, Redmond, WA) to evaluate both the expected rate of cancers missed at index colonoscopy and the rate of incident cancers that developed from missed adenomatous
Expected Rate of Missed Colorectal Cancers at Baseline Colonoscopy in a Screening Population
In the base-case analysis, at index colonoscopy a polyp containing cancer was missed in 0.7 per 1000 persons (Table 2). Seventy percent of missed cancers were attributed to missed lesions of 10 mm or larger (0.5 per 1000 persons). When applying the most conservative assumptions, a low miss rate (2% for adenomas ≥10 mm) and low cancer prevalence in adenomas (4% for adenomas ≥10 mm), the rate of missed cancers would decrease to 0.1 per 1000 persons. In that scenario all cancer cases would be
Discussion
Our model determined the expected rate of interval CRC after a screening colonoscopy resulting either from a missed cancer at baseline or an adenoma that transitioned to cancer in a short interval. We used available information on adenoma miss rates and the prevalence of cancer in adenomas by size and made plausible assumptions about transition rates from adenoma to cancer during the follow-up period. We calculated that a total of 1.8 per 1000 persons undergoing a screening colonoscopy would
Acknowledgments
The authors thank Douglas Rex from the Indiana University School of Medicine, Indianapolis, IN, for providing additional details on polyp histology from his study published in 2009.23 The authors thank the following members of the VA outcomes groups at the VA Medical Center in White River Junction, Vermont, for their support: H. Gilbert Welch, Brenda Sirovich, Robin Larson, Lisa Schwartz, and Steven Woloshin.
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Conflicts of interest The authors disclose no conflicts.
Funding This material is the result of work supported with resources and the use of facilities at the VA Medical Center, White River Junction, Vermont. Dr Robertson’s work is supported by a VA HSR&D Career Development Award. The contents of this article do not represent the views of the Department of Veterans Affairs or the United States Government.