Introduction Colonoscopy is the “gold standard” approach to investigating symptoms in relation to the colon. However, recent literature has shown that colonoscopy as a diagnostic test for colorectal cancer is far from perfect with a cancer missed rate of 8.6% in the UK. We aim to identify the rate of colorectal cancers diagnosed following a negative flexible sigmoidoscopy and/or colonoscopy and to explore contributing factors.

Methods This is a retrospective case analysis investigating all patients who received a diagnosis of colorectal cancer over a five-year period (2010–2015). We used our local clinical databases in identifying those patients who had negative flexible sigmoidoscopy and/ or colonoscopies but subsequently received a diagnosis of colorectal cancer.

Results 368 (Females 156; males 167; average age 76.71) patients were included in the initial sample. Of those 45 were excluded as an initial endoscope examination was not carried out and the cancers were identified by other means. Of 368 patients who were diagnosed with colorectal cancer, 35 (10.83%) had a previously normal endoscopic examination (19 flexible sigmoidoscopy; 16 colonoscopy)

Conclusion This research has shown that despite being the gold standard, colonoscopy as a diagnostic test for colorectal cancer is still far from perfect. In keeping with current research there appears to be a missed rate in detection of colorectal cancers, polyps and adenomas. Factors contributing to missed lesions are thought to be the presence of >2 lesions, lesions present in the left side of the colon, withdrawal time where longer withdrawal time was associated with higher lesion detection rate. Furthermore the smaller the lesion the lower the detection rate on colonoscopy (missed rate: 6% in adenomas >1 cm; 27% in adenomas <5 mm). It is worth bearing in mind that endoscopic procedures are very dependant on operator experience. We recommend longer and more rigorous training in endoscopic procedures and strongly advise following the standardised reporting systems in place.

References 1 Rex DK, Cutler CS, Lemmel GT, Rahmani EY, Clark DW, Helper DJ, Lehman GA, Mark DG. Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies. Gastroenterology 1997;112(1):24–8.

2 Barclay RL, Vicari JJ, Doughty AS, Johanson JF, Greenlaw RL. Colonoscopic withdrawal times and adenoma detection during screening colonoscopy. New England Journal of Medicine 2006;355:2533–2541.

Disclosure of Interest None Declared