title: How do colorectal cancers develop?
abstract: BACKGROUND
  The aim of this study was to reveal (1) whether a flat adenoma is the precursor of a flat cancer and (2) the more frequent pathway in colorectal cancer development-a flat cancer or a polypoid cancer.
  
  
  METHODS
  Clinical features and histologic characteristics of 97 flat early cancers, 138 polypoid early cancers, 60 advanced cancers involving the muscularis propria, and 185 flat adenomas were investigated.
  
  
  RESULTS
  Of the flat cancers, 89.7% were not accompanied by residual adenoma and are considered to have arisen de novo. The distribution of flat adenomas and flat cancers was significantly different, and a follow-up of flat adenomas did not reveal any rapid growth or carcinomatous changes in the flat adenomas. The shape of advanced cancers involving only the muscularis propria almost matches that of flat early cancers. Fifty-two of 97 flat cancers and 19 of 138 polypoid cancers invaded the submucosal layer.
  
  
  CONCLUSIONS
  Flat adenomas are not considered to be precursors of flat cancers. Advanced cancers of the large intestine originate mainly from flat cancers arising de novo. The percentage of the advanced cancers that originate from flat cancers is estimated to be 71.2% (52 of 52 +/- 19) at a minimum.
authors.affiliation: Third Department of Surgery, University of Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kuramoto
authors.forename: T
authors.initials: T
authors.lastname: Oohara
mesh_terms: D000236:Adenoma / Q000145:classification / Q000473:pathology*; D015179:Colorectal Neoplasms / Q000145:classification / Q000473:pathology*; D018450:Disease Progression; D005500:Follow-Up Studies; D006801:Humans