Original article
Colorectal Cancers Found After a Complete Colonoscopy

https://doi.org/10.1016/j.cgh.2006.07.012Get rights and content

Background & Aims: The incidence of colorectal cancer in patients undergoing colonoscopic surveillance is higher than previously thought. A better understanding of interval cancers is needed to improve surveillance strategies. The objectives of this study were to determine whether interval colorectal cancers were associated with an inadequate earlier colonoscopy, incomplete polypectomy, or aggressive biologic behavior. Methods: We searched our institution’s cancer registry. Interval cancers were defined as colorectal cancers that developed within 5 years of a complete colonoscopy. These were frequency matched in a 1:2 ratio to patients with sporadic cancers, which were defined as colorectal cancers diagnosed on a patient’s first recorded colonoscopy. Patient, colonoscopy, and tumor characteristics of interval and sporadic cancers were compared. Results: Of the 830 colorectal cancers diagnosed during the study period, 45 patients developed an interval cancer (5.4%; 95% confidence interval, 4.1%–7.2%). Twenty-seven percent of interval cancers developed at previous polypectomy segments, and location of polypectomy segments was predictive of the location of subsequent interval cancers. Interval cancers were 3 times more likely to occur in the right colon and were smaller in size than sporadic cancers. Quality of bowel preparation, individual endoscopist, endoscopist experience, and trainee involvement were not associated with interval cancers. No difference in TNM stage at diagnosis, histologic type or grade, carcinoembryonic antigen level, or 5-year survival was found between interval and sporadic cancers. Conclusions: Incomplete polypectomy might play an important role in the development of interval colorectal cancer. No association between other colonoscopy-related factors or tumor characteristics and interval cancers was found.

Section snippets

Patient Selection and Data Collection

All veterans with a diagnosis of cancer at the Minneapolis Veteran Affairs Medical Center are accessioned into a cancer registry and are monitored for lifetime follow-up. The registry currently has data on 34,738 patients with cancer and consistently maintains a >95% follow-up rate. We searched the cancer registry from January 1, 1991 to August 31, 2004, and identified all patients with incident colorectal cancer. We excluded those with familial adenomatous polyposis, hereditary non-polyposis

Results

During the specified period, 830 patients were diagnosed with colorectal cancer at the Minneapolis Veterans Affairs Medical Center and met entry criteria for the study. Of these, 45 patients developed colorectal cancers within 5 years of their most recent colonoscopy. These cancers were termed interval cancers and accounted for 5.4% (95% confidence interval [CI], 4.1%–7.2%) of all colorectal cancers diagnosed at our institution. Interval cancers were diagnosed on average 33.8 months after

Discussion

Of all colorectal cancers diagnosed at our institution, 5.4% developed within 5 years of the complete colonoscopy. Interval cancers were more likely to be located in the right colon and were smaller in size when compared with sporadic cancers. Twenty-seven percent of interval cancers occurred at a previous polypectomy segment, and there was a significant association between the location of polypectomy segments and the subsequent location of interval cancers. Factors that influence the quality

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    Supported in part by VA Clinical Science R&D Service (grant no. 04S-CRCOE-001) (M.S.S.).

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