Background: The natural behavior of flat low-grade (LGD) and indefinite dysplasia (IND) in patients with inflammatory bowel disease (IBD) remains uncertain and seems to be dependent on the interpretation of the pathologist. We studied the progression rate of flat LGD and IND to advanced neoplasia (high-grade dysplasia [HGD] or colorectal cancer [CRC]) before and after histopathological review by a panel of gastrointestinal expert pathologists. Methods: A nationwide pathology database was used to identify IBD patients with dysplasia in six Dutch university medical centers between 1990 and 2006. Medical charts of patients with recorded flat LGD or IND were reviewed. Histological slides from three university medical centers were reviewed by a panel of three expert gastrointestinal pathologists. Results: We identified 113 flat LGD patients and 26 flat IND patients. Advanced neoplasia was found in 18 flat LGD patients (16%) after a median follow-up of 48 months, resulting in a 5-year progression rate of 12%. Five IND patients (19%) developed advanced neoplasia after a median follow-up of 24 months, resulting in a 5-year progression rate of 21%. Review of 1547 histological slides from 87 patients resulted in an increase of the 5-year progression rate of flat LGD to advanced neoplasia to 37%, whereas the progression rate of IND decreased to 5%. Conclusions: A diagnosis of flat LGD that is confirmed by a panel of expert gastrointestinal pathologists is associated with a substantial risk of progression to advanced neoplasia, while confirmed IND is associated with a low risk of progression. (Inflamm Bowel Dis 2010;)

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Keywords colorectal cancer, dysplasia, inflammatory bowel disease
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