The inception of the NHS Bowel Cancer Screening Programme (BCSP) in England in 2006 highlighted that the differential diagnosis between the presence of epithelial misplacement and adenocarcinoma occurring in colorectal adenomas is problematic. The Pathology Expert Board (EB) was created to facilitate review of difficult cases by a panel of three experienced gastrointestinal pathologists. This script describes a review of the work of the EB over a 4-year period (2017-2020).

430 polyps were referred to the EB from 193 pathologists and 76 hospitals during this time. The EB diagnosis was benign in 67%, malignant in 28% and equivocal in 2% (with no consensus in the remainder). The most common diagnosis change made by the EB was from malignant to benign – made in 50% of polyps referred with an initially malignant diagnosis. The level of agreement between the individual EB members was ‘good’ (kappa score 0.619) but that between the EB and the referring diagnosis was ‘poor’ (kappa score 0.149). Data from one EB member indicated that the presence of lamina propria, features of torsion and cytological similarity between the superficial and deep glands were predictors of a benign diagnosis, while the presence of irregular neoplastic glands, a desmoplastic reaction and lymphovascular invasion were commonly observed features in a malignant diagnosis.

Diagnostic agreement between EB members is better than that between the EB and referring pathologists. There was a consistent trend for the EB to change diagnoses from malignant to benign.