title: Flat and depressed colonic neoplasms: a prospective study of 1000 colonoscopies in the UK.
abstract: BACKGROUND
  Flat and depressed colorectal tumours were originally thought to be unique to the Japanese population. Recently there have been reports of flat and depressed lesions in western countries but they have been thought to be uncommon.
  
  
  METHODS
  In this prospective study, 1000 consecutive patients attending for routine colonoscopy were examined for flat or depressed lesions. The examinations were done by one European colonoscopist using methods developed in Japan.
  
  
  RESULTS
  321 adenomas were found: 202 (63%) were polypoid, 36% (117) were flat and 2 (0.6%) appeared depressed. Most adenomas contained areas of mild or moderate dysplasia but 10% (31) were severely dysplastic. Six Dukes' A adenocarcinomas were identified together with 25 more advanced adenocarcinomas. The likelihood of Dukes' A cancer or severe dysplasia increased from 4% (3/70) in small flat lesions, to 6% (9/154) in small polyps, 16% (8/50) in larger polyps, 29% (14/49) in large flat lesions, and 75% (3/4) in depressed lesions. 54% (20/37) lesions containing severe dysplasia or Dukes' A carcinoma were flat or depressed.
  
  
  CONCLUSIONS
  The polyp-carcinoma hypothesis prompts colonoscopists to search only for polypoid lesions when screening for cancer, and many early colorectal neoplasms may therefore be missed. Colonoscopists require training in the recognition of flat and depressed lesions to detect colorectal tumours in the early stages.
authors.affiliation: Centre for Digestive Diseases, The General Infirmary, Leeds. BJR@firstnet.co.uk
authors.forename: B J
authors.initials: BJ
authors.lastname: Rembacken
authors.forename: T
authors.initials: T
authors.lastname: Fujii
authors.forename: A
authors.initials: A
authors.lastname: Cairns
authors.forename: M F
authors.initials: MF
authors.lastname: Dixon
authors.forename: S
authors.initials: S
authors.lastname: Yoshida
authors.forename: D M
authors.initials: DM
authors.lastname: Chalmers
authors.forename: A T
authors.initials: AT
authors.lastname: Axon
mesh_terms: D000230:Adenocarcinoma / Q000453:epidemiology / Q000473:pathology*; D000236:Adenoma / Q000453:epidemiology / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003111:Colonic Polyps / Q000453:epidemiology / Q000473:pathology*; D003113:Colonoscopy / Q000592:standards*; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000473:pathology*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D006113:United Kingdom / Q000453:epidemiology