[Conventional and non-conventional dysplasia in patients with inflammatory bowel disease].

Compared to the general population, patients with inflammatory bowel disease (IBD), both ulcerative colitis (UC) or Crohn's disease (CD), are at increased risk of developing some cancers, particularly colorectal cancers (CRC). CRCs, the vast majority of which are adenocarcinomas, develop from a precancerous lesion called dysplasia (or intraepithelial neoplasia) via an inflammation-dysplasia-adenocarcinoma sequence. The advancements of new endoscopic techniques, including visualisation and resection techniques, has led to a reclassification of dysplasia lesions into visible and invisible lesions and their therapeutic management, with a more conservative approach to the colorectal setting. In addition, besides conventional dysplasia, of intestinal phenotype, classically described in IBD, non-conventional dysplasias (as opposed to conventional dysplasia of intestinal phenotype) are now described, including at least seven subtypes. Recognition of these unconventional subtypes, which are still poorly known from pathologists, is becoming crucial, as some of these subtypes appear to be at high risk of developing advanced neoplasia (i.e. high-grade dysplasia or CRC). This review briefly describes the macroscopic features of dysplastic lesions in IBD, as well as their therapeutic management, followed by the clinicopathological features of these dysplastic lesions, with particular emphasis on the new subtypes of unconventional dysplasia, both from a morphological and molecular point of view.