Consideration of adequate follow up period to avoid interval cancer

(Background and Aims)Colorectal cancers diagnosed with a few years after a previous colonoscopy can arise from missed lesions or development of a new tumor and recently such cancers are reported as interval cancer. The most severely follow up period is recommended to perform surveillance colonoscopy every 3 years.(Methods)We analyzed 59125 cases/43210 patients who underwent colonoscopy. Patients were defined as having an interval cancer (IC) if they detected colorectal submucosal invasive or deeper invasive cancer within 36months from index colonoscopy. Another cancer was defined as a non-interval cancer (NIC). We investigated the clinical difference between IC and NIC.(Result)We identified 35 cases of IC and 1030 cases of NIC. IC/NIC were male;82.9%/65.3% (p=0.03), diameter(T1stage);15.9mm/21.1mm (p=0.002), diameter(T2stage);30.6mm/51.0mm(p=0.002), right colon;51.4%/32.8%(P=0.02), respectively. At the index colonoscopy, IC/NIC were three or more tumor coexistence;57.1%/36.7%(p=0.012), existing of tumor over10mm;45.7%/19.0%(p=0.001), mean insertion time;10.2min/7.1min(p=0.003), respectively. (Conclusion)Out of these characteristics in IC, three or more tumor coexistence, existing of tumor over10mm, and long insertion time could be predictive factors at the index colonoscopy. Therefore if physicians recognized these factors at index colonoscopy, follow up period should be shortening less than 3years.