Aim: To determine the inter-observer variation in the histological diagnosis of colorectal polyps. Methods and results: Four hundred and forty polyps were randomly selected from a colorectal cancer screening programme. Polyps were first evaluated by a general (324 polyps) or expert (116 polyps) pathologist, and subsequently re-evaluated by an expert pathologist. Conditional agreement was reported, and inter-observer agreement was determined using kappa statistics. In 421/440 polyps (96%), agreement for their non-adenomatous or adenomatous nature was obtained, corresponding to a very good kappa value of 0.88. For differentiation of adenomas as non-advanced and advanced, consensus was obtained in 266/322 adenomas (83%), with a moderate kappa value of 0.58. For the non-adenomatous or adenomatous nature, both general and expert pathologists, and expert pathologists between each other, showed very good agreement {kappa values of 0.89 [95% confidence interval (CI) 0.83-0.95] and 0.86 (95% CI 0.73-0.98), respectively}. For categorization of adenomas as non-advanced and advanced, moderate agreement was found between general and expert pathologists, and between expert pathologists [kappa values of 0.56 (95% CI 0.44-0.67) and 0.64 (95% CI 0.43-0.85), respectively]. Conclusions: General and expert pathologists demonstrate very good inter-observer agreement for differentiating non-adenomas from adenomas, but only moderate agreement for non-advanced and advanced adenomas. The considerable variation in differentiating non-advanced and advanced adenomas suggests that more objective criteria are required for risk stratification in screening and surveillance guidelines.

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Keywords Colorectal cancer screening, Colorectal polyps, Histological diagnosis, Interobserver variation
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Journal Histopathology
van Putten, P.M.A, Hol, L, van Dekken, H, van Krieken, J.H.J.M, van Ballegooijen, M, Kuipers, E.J, & van Leerdam, M.E. (2011). Inter-observer variation in the histological diagnosis of polyps in colorectal cancer screening. Histopathology, 58(6), 974–981. doi:10.1111/j.1365-2559.2011.03822.x