Challenging diagnostic issues in adenomatous polyps with epithelial misplacement in bowel cancer screening: five years' experience of the BCSP Expert Board

The diagnostic difficulties of differentiating epithelial misplacement from invasive cancer in colorectal adenomatous polyps have been recognised for many years. Nevertheless, the introduction of population screening in the UK has provided extraordinary diagnostic problems. Larger sigmoid colonic adenomatous polyps, those most likely to show epithelial misplacement, are specifically selected into such screening programmes because these polyps are likely to bleed and screening is based on the detection of occult blood. The diagnostic challenges associated with this particular phenomenon have necessitated the institution of an "Expert Board": this is a review of the first five years of its practice, during which time 256 polyps from 249 patients have been assessed. Indeed, the constitution of the Board has been with three pathologists because those pathologists do not necessary agree and a consensus diagnosis is required to drive appropriate patient management. However, this study has shown substantial levels of agreement between the three Expert Board pathologists whereby the ultimate diagnosis has been changed, from that of the original referral diagnosis, by the Board in half of all the polyps, in the substantial majority from malignant to benign. In 3% of polyp cases, the Expert Board consensus has been the dual diagnosis of both epithelial misplacement and adenocarcinoma, further illustrating the diagnostic difficulties. The Expert Board of the Bowel Cancer Screening Programme in the UK represents a unique and successful development for an extraordinary diagnostic conundrum created by the particular characteristics of bowel cancer screening.