title: Reappraisal of the so-called 'villous tumours' of the rectosigmoid, based on histological, immunohistochemical and genotypic features.
abstract: BACKGROUND
  Villous tumours of the rectosigmoid are historically defined as broad-based lesions associated with secretory diarrhoea.
  
  
  OBJECTIVE
  This study aimed to perform a reappraisal of these tumours, on the basis of newly introduced histological, immunohistochemical and molecular parameters.
  
  
  METHODS
  For this study, 22 villous tumours, diagnosed by endoscopic criteria (19 Paris 0-IIa, three Paris 0-Is), were evaluated according to WHO classification. Microsatellite instability status, KRAS and BRAF mutations, MGMT status of villous tumours and associated invasive carcinoma were determined.
  
  
  RESULTS
  The 22 villous tumours fell into four groups: 1) nine villous adenomas, 2) six tubulovillous adenomas, 3) three filiform traditional serrated adenomas, and 4) four traditional serrated adenomas with conventional dysplasia. Filiform serrated adenomas displayed a distinctive endoscopic protruding pattern (Paris 0-Is). Villous adenomas were strongly associated with secretory diarrhoea. All the villous tumours were microsatellite stable. Five tumours exhibited MGMT abnormalities. KRAS mutations were frequent in villous adenomas, whereas BRAF mutations were essentially detected in serrated lesions. Invasive carcinomas (n = 7) maintained the histopathological and molecular imprint of the prior villous tumour.
  
  
  CONCLUSIONS
  The rectosigmoid villous tumours are histologically and molecularly heterogeneous, including serrated neoplasias. Endoscopic and clinical findings are predictive of the histopathological diagnosis of some of these distinct entities.
authors.affiliation: CHU Nantes, Service d'Anatomie et Cytologie Pathologiques, Nantes, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Droy-Dupré
authors.affiliation: CHU Nantes, Service de Génétique Médicale, Nantes, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Küry
authors.affiliation: CHU Nantes, Service de Gastroentérologie, Nantes, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Coron
authors.affiliation: CHU Nantes, Service de Génétique Médicale, Nantes, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Bézieau
authors.affiliation: CHU Nantes, Service d'Anatomie et Cytologie Pathologiques, Nantes, France.
authors.forename: Christian L
authors.initials: CL
authors.lastname: Laboisse
authors.affiliation: CHU Nantes, Service d'Anatomie et Cytologie Pathologiques, Nantes, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Mosnier
keywords: Rectal neoplasms; endoscopy; microsatellite instability; serrated adenoma; villous tumour
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