title: Proportion of de novo cancers among colorectal cancers in Japan.
abstract: OBJECTIVE
  Adenomatous polyps are main precursors of colorectal cancers (CRCs). In Japan, de novo cancers, which do not arise from preexisting adenomas, are considered to account for a substantial number of CRCs, but the relative importance of de novo carcinogenesis remains controversial. This study estimated the proportion of de novo cancers among CRCs in Japan.
  
  
  METHODS
  The subjects were persons 40-79 years of age who were relatively similar to those in the general population. The subjects underwent colonoscopy between 1997 and 2001. Early cancers among CRCs detected in this study were classified as de novo cancers or polyp cancers derived from adenomas. The age-specific incidence of the early CRCs was calculated, and the proportion of de novo cancers was estimated. The lifetime risk of early CRCs was estimated.
  
  
  RESULTS
  The study group comprised 14,817 persons. CRCs were diagnosed in 189 subjects, including 83 early cancers. There were no differences with regard to size and location between de novo cancers and polyp cancers, but morphology differed. Eighty-four percent (16/19) of de novo cancers were flat elevated or depressed. The expected lifetime risk of developing early CRCs was 5.27% for men and 3.21% for women. Among persons with early cancers, the expected probabilities of developing de novo cancer were 18.6% for men, 27.4% for women.
  
  
  CONCLUSIONS
  De novo cancers account for a considerable proportion in Japan. This information suggests that the recommended interval for colonoscopic examination in Japan should be shorter than that in the United States.
authors.affiliation: Hattori GI Endoscopy and Oncology Clinic, Kumamoto, Japan. gotouh7@mac.com
authors.forename: Hideyo
authors.initials: H
authors.lastname: Goto
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Oda
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Murakami
authors.forename: Tomofumi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Hasuda
authors.forename: Sayoko
authors.initials: S
authors.lastname: Goto
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Sasaki
authors.forename: Shotaro
authors.initials: S
authors.lastname: Sakisaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hattori
mesh_terms: D000328:Adult; D000368:Aged; D003111:Colonic Polyps / Q000453:epidemiology / Q000473:pathology; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000473:pathology; D005260:Female; D006801:Humans; D015994:Incidence; D007413:Intestinal Mucosa / Q000473:pathology; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011230:Precancerous Conditions / Q000453:epidemiology* / Q000473:pathology; D012189:Retrospective Studies; D012307:Risk Factors; D017678:Sex Distribution