Colonoscopy with detection and removal of
neoplasms strongly reduces risk of
colorectal cancer (CRC). Nevertheless,
CRCs occur after colonoscopic polypectomy. We assessed agreement beyond chance of location of
polyps detected at colonoscopy and of subsequent
CRCs to estimate the share of
cancers that might be due to field effects or
neoplasm recrudescence. In a population-based case-control study conducted in Germany (3,148 cases), detailed history and results of colonoscopies conducted within 10 years before
cancer diagnosis were obtained by interview and from medical records. We determined the observed proportion of
cancers for which a
polyp had been detected at the same colorectal subsite at the preceding colonoscopy and compared it to the proportion expected by chance. A total of 155 cases with physician validated
polyp detection at the preceding colonoscopy were identified. Among 148 cases with
cancer restricted to a single subsite, 43 (29.1%) had a
polyp detected in the same colorectal subsite at the preceding colonoscopy. Agreement of location of
cancer occurrence and preceding
polyp detection would have been expected by chance for 27 cases, and agreement beyond chance was estimated to account for 16 cases (10.8%, 95% confidence interval 2.7%-19.3%). Our study suggests that less than one of nine
CRCs occurring within 10 years after colonoscopy with
polyp detection may be due to field effects or
polyp recrudescence.