Introduction Colonoscopy and flexible sigmoidscopy are the primary tools for diagnosis of CRC, although they have false negative rates of 2–6%.¹ The aim of this study was to estimate how frequently lower GI endoscopy might have failed to detect cancer within 36 months preceding a confirmed diagnosis of CRC.

Methods We identified 253 patients diagnosed with CRC between Sep 2010 – Aug 2012 from the database of cellular pathology in Cardiff and Vale University Health Board. Medical records were reviewed for the results of colonoscopy, flexible sigmoidscopy, histology and CT imaging. Patients with missed cancer were those who had had a ‘normal’ (if no cancer discovered) lower GI endoscopy procedure 1–36 months before diagnosis. We examined the characteristics that might be risk factors for missed CRC.

Results Among the 253 patients included in the study, cancer was located in the rectosigmoid colon (78.5%), descending colon (2.7%), splenic flexure (1.9%), transverse colon (4.3%), hepatic flexure (1.1%) and right colon (9.4%). We identified 10 (5 females, 5 males, mean age 80 years, range 42–92) patients (3.9%) who had had colonoscopy and/or flexible sigmoidscopy that had not shown CRC 1–36 months prior to the final diagnosis. In the missed cancer group only one flexible sigmoidscopy was incomplete due to suboptimal bowel preparation and difficult sigmoid bend. Nine patients had false negative lower GI endoscopy. The median diagnostic delay was 13.6 months (1–36). Two of the missed cancers were diagnosed with Dukes’ C colon cancer, one with Dukes’ D colon cancer and one presented with emergency complications due perforation. Of the ten missed cancers, eight were in rectosigmoid colon, one in the transverse colon and one in the ascending colon.

Conclusion Bressler et al reported 2–6% missed CRC at colonoscopy performed 6–36 months prior to a final diagnosis of cancer.¹ Our miss rates are in line with previous studies. However, the available literature suggests that lesion miss rate is higher for proximal colonic tumours. In our study, the missed cancers were predominantly in the rectosigmoid colon (3.1%) and were minimal in the right colon (0.4%). The reasons for missed cancers in our study are likely related to incomplete procedure, suboptimal bowel preparation, inadequate technique, failure to recognise flat lesions and diverticulosis. Optimal withdrawal technique, good luminal view, frequent position change, high quality bowel prep and adequate time for inspection are of utmost importance to minimise the rate of missed CRC.

Disclosure of Interest None Declared.

Reference

1. Bressler B, et al. Rates of new or missed colorectal cancer after colonoscopy and their risk factors: a population–based study. Gastroenterology 2007; 132(1):96–102