Characteristics of Advanced Neoplasia Detected within 3 Years after Colonoscopy

[Background and aim] Colorectal cancer (CRC) can be prevented by removing precancerous lesions via colonoscopy. However, the effectiveness of colonoscopy to prevent CRC seems to be limited in the proximal colon. Research suggests that many cases of post-colonoscopy CRC are attributable to missed lesions in the previous colonoscopy. This study aimed to clarify the characteristics of advanced neoplasia that might be missed on screening colonoscopy and were detected later (post-colonoscopy lesions). [Patients and Methods] From April 2010 to September 2013, we performed 10,632 colonoscopies. Of these, we retrospectively analyzed the location and morphology of 934 advanced neoplasias.[Results] Among 934 advanced neoplasias, 144 lesions (15.4%) were detected 0.5-3.5 years after colonoscopy. The percentage of post-colonoscopy lesions in the right and left colon was 19.4% (68/350) and 13.0% (76/584), respectively (p < 0.01). The percentage of post-colonoscopy lesions in advanced CRCs (>T2 lesions) was 1.0% (2/204), which was excluded from the morphological discussion. The percentage of post-colonoscopy lesions in polypoid, flat, depressed, laterally spreading tumors granular type (LST-G), and laterally spreading tumors non-granular type (LST-NG) lesions was 18.3% (109/597), 38.2% (12/34), 28.6% (2/7), 10.9% (5/46), and 28.3% (13/46), respectively (p = 0.01).[Conclusions] The findings revealed that right-side, flat, depressed type, and LST-NG lesions tended to be more often detected after colonoscopy. Therefore, such lesions should be paid extra attention to during screening and surveillance colonoscopy.