Aetiology and prevalence of post-colonoscopy colorrectal cancer.

Background: Colonoscopy is the gold standard for the detection and prevention of colorectal cancer (CRC). However, some individuals are diagnosed with CRC soon after a previous colonoscopy.

Aims: To evaluate the rate of new onset or missed CRC after a previous colonoscopy and to study potential risk factors.

Methods: Patients in our endoscopy database diagnosed with CRC from March 2004 to September 2011 were identified, selecting those with a colonoscopy performed within the previous 5years. Medical records included age, gender, comorbidities and colonoscopy indication. Tumour characteristics studied were localization, size, histological grade and TNM stage and possible cause. These patients were compared with those diagnosed with CRC at their first endoscopy (sporadic CRC-control group).

Results: A total of 712 patients with CRC were included; 24 patients (3.6%) had undergone colonoscopy within the previous 5 years (50% male, 50% female, mean age 72). Post-colonoscopy CRCs were attributed to: 1 (4.2%) incomplete colonoscopy, 4 (16.6%) incomplete polyp removal, 1 (4.2%) failed biopsy, 8 (33.3%) 'missed lesions' and 10 (41.7%) new onset CRC. Post-colonoscopy CRCs were smaller in size than sporadic CRCs (3.2cm vs. 4.5cm, P<.001) and were mainly located in the proximal colon (63% vs. 35%, P=.006); no difference in histological grade was found (P=.125), although there was a tendency towards a lower TNM stage (P=.053).

Conclusions: There is a minor risk of CRC development after a previous colonoscopy (3.6%). Most of these (58.4%) are due to preventable factors. Post-colonoscopy CRCs were smaller and mainly right-sided, with a tendency towards an earlier TNM stage.