Original article—alimentary tract
Colorectal Cancers Detected After Colonoscopy Frequently Result From Missed Lesions

https://doi.org/10.1016/j.cgh.2010.06.028Get rights and content

Background & Aims

Colorectal cancers (CRCs) that are detected in patients who have received colonoscopies (interval cancers) arise from missed lesions, incomplete resections of adenomas, or de novo. We estimated rates of interval cancer from missed lesions.

Methods

Adenoma miss rates, cancer prevalence among patients with adenoma (based on size), and rates of adenoma-to-cancer transitions were estimated from the literature. We used a model to apply these risk estimates to a hypothetical average-risk population that received screening colonoscopies. We calculated the proportion of individuals with tumors missed at the baseline colonoscopy and tumors that arose from missed adenomas during a 5-year follow-up period. Sensitivity analyses were performed to assess robustness.

Results

We found that 0.7 per 1000 persons undergoing a screening colonoscopy had a cancer that was missed at the baseline colonoscopy and an additional 1.1 per 1000 subsequently developed cancer from a missed adenoma. Therefore, the expected rate of individuals with CRC, based on missed adenomas, was 1.8 per 1000 persons within 5 years. By using the most conservative assumptions—a low miss rate and low prevalence of cancer in adenomas—0.5 per 1000 persons would have a detectable CRC within 5 years after a screening colonoscopy. In contrast, using the highest reported miss rates and cancer prevalence, CRCs from missed lesions would occur in 3.5 per 1000 screened persons.

Conclusions

A significant number of patients undergoing a screening colonoscopy that did not detect cancer actually have a malignant lesion or adenoma that could progress in a short interval. Most interval cancers might reflect missed rather than new lesions. Improving adenoma detection could reduce the rate of interval cancers.

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.

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