Introduction One of the biggest advantages of colonoscopy is the detection or prevention of early colorectal cancer (CRC). However, it is associated with a varying risk of missing CRC (2–6%). PCCRC may be due to missed pathology (poor technique, incomplete colonoscopy, inadequate bowel preparation, flat lesions) at prior colonoscopy, previous incomplete polypectomy or rapid growth (interval cancers). PCCRC is associated with female gender, advancing age, right-sided lesions and a history of diverticular disease.

Methods To assess the rate of PCCRC at a single tertiary endoscopy centre. All CRC related data were collected prospectively and stored in the centre's CRC database. Only those patients who had a colonoscopy at this centre were included in the study. A retrospective analysis was performed of patients diagnosed with CRC between October 2008 and October 2010 who had undergone a ‘negative’ colonoscopy within three years of their diagnosis. Data regarding age, sex, site and tumour morphology were collected and analysed.

Results 578 patients were diagnosed with CRC in the time-frame analysed. Of these, 16 (2.7%) had a ‘negative’ colonoscopy within three years of diagnosis (12.1 months (1–33)). 10/16 (62.5%) were female. Mean age at diagnosis was 63.2 years (37–89). 50% (8/16) were right colonic lesions. In 3/16 (18.7%) cases, the colonoscopy was incomplete either due to severe diverticular disease (n=2) or poor bowel preparation (n=1). In all three cases (elderly females with right-sided CRCs) appropriate urgent follow-up investigations were arranged by the endoscopist. One PCCRC was found at the site of a previous polypectomy. In a further three cases, abnormal areas were identified but the actual CRC, missed. However, appropriate follow up was organised in these cases. Four PCCRCs were found in diverticular segments and one was a flat lesion. 4/16 (25%) PCCRCs were genuinely missed at previous colonoscopy.

Conclusion The results of this retrospective analysis suggest that the postcolonoscopy CRC rate at this centre was comparable to that reported in other published literature and highlights the risk factors for PCCRC.