Post-colonoscopy colorectal cancers in a national FIT-based CRC screening program

Background and study aims: Post-colonoscopy colorectal cancers (PCCRCs) decrease the effect of colorectal cancer (CRC) screening programs. To enable PCCRC incidence reduction on the long-term we classified PCCRCs diagnosed after colonoscopies performed in a fecal immunochemical test (FIT-) based screening program. Patients and methods: PCCRCs diagnosed after colonoscopies performed between 2014-2016 for positive FIT in the Dutch CRC screening program were included. PCCRCs were categorized according to the World Endoscopy Organization consensus statement into a) interval PCCRC (diagnosed before the recommended surveillance), b) non-interval-type-A (diagnosed at the recommended surveillance interval), c) non-interval-type-B (diagnosed after the recommended surveillance interval), or d) non-interval-type-C (diagnosed after the intended recommended surveillance interval, but not applied due to comorbidity). The most probable etiology was determined by root-cause analysis. Tumor stage distributions were compared between categories. Results: 116,362 colonoscopies were performed after positive FIT with 9,978 screen-detected CRCs. During follow-up, 432 PCCRCs were diagnosed. The 3-year PCCRC rate was 2.7%. PCCRCs were categorized as interval (53.5%), non-interval-type-A (14.6%), non-interval-type-B (30.6%), and non-interval-type-C (1.4%). Interval PCCRCs had as most common etiology a possible missed lesion with adequate examination (73.6%) and were more often diagnosed at an advanced stage (stage III/IV, 53.2%) compared to non-interval-type-A (15.9%, p<0.001) and non-interval-type-B (40.9%, p=0.025) PCCRCs. Conclusions: The 3-year PCCRC rate was low in this FIT-based CRC screening program. Approximately half of PCCRCs were interval PCCRCs. These were mostly caused by missed lesions and were diagnosed at more advanced stage. This emphasizes the importance of high-quality colonoscopy with optimal polyp detection.