Post-colonoscopy colorectal cancer rate in the era of highdefinition colonoscopy

AIM To investigate the post-colonoscopy colorectal cancer(PCCRC) rate for high-definition(HD) colonoscopy compared with that for standard-definition colonoscopy reported previously.METHODS Using medical records at Sano Hospital(SH) and Dokkyo Medical University Koshigaya Hospital(DMUKH), we retrospectively obtained data on consecutive patients diagnosed as having CRC between January 2010 andDecember 2015. The definition of PCCRC was diagnosis of CRC between 7 and 36 mo after initial high-definition colonoscopy that had detected no cancer, and patients were divided into a PCCRC group and a non-PCCRC group. The primary outcome was the rate of PCCRC for HD colonoscopy. The secondary outcomes were factors associated with PCCRC and possible reason for occurrence of early and advanced PCCRC.RESULTS Among 892 CRC patients, 11 were diagnosed as having PCCRC and 881 had non-PCCRC. The PCCRC rate was 1.7%(8/471) at SH and 0.7%(3/421) at DMUKH. In comparison with the non-PCCRC group, the PCCRC group had a significantly higher preponderance of smaller tumors(39 mm vs 19 mm, P = 0.002), a shallower invasion depth(T1 rate, 25.4% vs 63.6%, P = 0.01), a non-polypoid macroscopic appearance(39.0% vs 85.7%, P = 0.02) and an earlier stage(59.7% vs 90.9%, P = 0.03). Possible reasons for PCCRC were 'missed or new' in 9 patients(82%), 'incomplete resection' in 1(9%), and 'inadequate examination’' in 1(9%). Among 9 'missed or new' PCCRC, the leading cause was non-polypoid shape for early PCCRC and blinded location for advanced PCCRC.CONCLUSION The PCCRC rate for HD colonoscopy was 0.7%-1.7%, being lower than that for standard-definition colonoscopy(1.8%-9.0%) reported previously employing the same methodology.