Introduction Little is known about the rates or reasons for missing diagnosis of bowel cancer in outpatients. This study determined the number of missed cancers by flexible sigmoidoscopy (FS), barium enema (BE), colonoscopy, CT colonography (CT) and in patients not having whole colonic imaging (WCI) after a normal FS.

Method Retrospective cohort analysis using clinical data collected prospectively for 22 years (1986–2007) in a colorectal outpatient clinic in Portsmouth. 29005 patients were analysed. Missed cancers were detected by referral back to clinic, local audit for NBOCAP and comparison with the regional Cancer Registry.

Results 1626 patients had bowel cancer. 66.1% (19174/29005) of all patients in the study did not have WCI. 13.8% (3993) had colonoscopy, 17.9% (5206) had BE and 883 (latter 8 years) had CT. 3.9% (63/1626) of cancers were missed; 21 distal (rectum and sigmoid), 41 proximal and 1 unknown site. 1.6% (21/1333) or 1:63 of distal cancers were missed by FS. Twenty-one of all missed cancers were subsequently diagnosed within 1 year (50–358 days) of the outpatient clinic, twenty within 1–2 years and twenty-two between 2–3 years.

Twenty-two proximal cancers were subsequently diagnosed with cancer after a normal FS and no WCI, which means the incidence of cancer in this group of patients was 0.1% (22/18252).

Conclusion A policy of outpatient FS with selective WCI resulted in a low rate of missed cancers. The replacement of BE by Colonoscopy and CT should greatly reduce the numbers of missed cancers in those having WCI. Strict diagnostic strategies are required to avoid excessive delay in diagnosis of the few with cancer without over investigation of patients with transient symptoms from benign disease.

Disclosure of interest None Declared.