Colorectal cancer detected up to 5 years after a ‘normal’ colonoscopy/ flexible sigmoidoscopy

Introduction Lower GI endoscopy has replaced barium enema as the primary method for diagnosis of colorectal cancer (CRC), but has an inherent miss rate. The aim was to estimate how frequently lower GI endoscopy might have failed to detect cancer during the 5 years preceding a final diagnosis of CRC. Methods 273 patients were identified from cancer registry with CRC from April 2007 to March 2009. Records were reviewed for the results of colonoscopy and flexible sigmoidoscopy 6 months to 5 years prior to their diagnosis of cancer. Results Among the 273 patients, we identified 10 patients (3.7%) who had colonoscopy and /or flexible sigmoidoscopy that had not shown CRC prior to the final diagnosis. In the missed cancer group three cases were incomplete and eight were false negative with a median diagnostic delay of 36 months (range 12–60). 70% of the missed cancer group were diagnosed with Dukes9 C colon cancer and 30% presented with emergency complications. Conclusion A recent study by Bressler et al suggested that up to 4% of cancers may be missed at colonoscopy. Our miss rates are in line with previous studies. The reasons why cancers were missed relate to incomplete colonoscopy, poor bowel preparation, inadequate technique, prior incomplete polypectomy, failure to recognise flat lesions, misinterpretation of what was seen and failure to arrange alternative tests in patients with incomplete tests.