title: Flat adenoma as a precursor of colorectal carcinoma in hereditary nonpolyposis colorectal carcinoma.
abstract: BACKGROUND
  Because flat adenoma shows a higher malignancy rate compared with other types of polyps, it is considered to play an important role in the carcinogenesis of colorectal carcinoma. In the present study, we examined flat adenomas in hereditary nonpolyposis colorectal carcinoma (HNPCC) patients.
  
  
  METHODS
  Nine HNPCC patients who presented with flat adenomas were examined. All patients underwent either surgery or endoscopic polypectomy for colorectal carcinoma and/or adenoma. In all patients, annual colonoscopy had been performed once a year throughout the follow-up period after the initial treatment. When colorectal polyps were detected during follow-up colonoscopy, all lesions were endoscopically excised. Clinicopathologic features and microsatellite instability of both malignant lesions and adenomas were examined.
  
  
  RESULTS
  Thirteen malignant lesions were detected: seven advanced carcinomas and six early carcinomas. Among 4 early carcinomas with submucosal invasion, 3 lesions (75%) were categorized as superficial type, with a configuration similar to flat adenoma. The frequency of flat adenoma was strikingly high in HNPCC patients in the present study. Among 73 polyps detected, 37 (50.7%) were flat adenomas. Both malignant lesions and flat adenomas had proximal predominance, 61.5% and 59.5%, respectively. Eleven of 15 lesions (73.3%) showed replication error.
  
  
  CONCLUSIONS
  These results suggest the importance of flat adenoma as a precursor of colorectal carcinoma in some groups of HNPCC patients. Further study is essential to elucidate the natural history of flat adenomas in HNPCC patients.
authors.affiliation: First Department of Surgery, University of Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Watanabe
authors.forename: T
authors.initials: T
authors.lastname: Muto
authors.forename: T
authors.initials: T
authors.lastname: Sawada
authors.forename: M
authors.initials: M
authors.lastname: Miyaki
mesh_terms: D000236:Adenoma / Q000235:genetics / Q000473:pathology* / Q000601:surgery*; D011125:Adenomatous Polyposis Coli / Q000235:genetics / Q000473:pathology* / Q000601:surgery*; D000368:Aged; D000369:Aged, 80 and over; D002896:Chromosomes, Human, Pair 6; D003111:Colonic Polyps / Q000235:genetics / Q000473:pathology / Q000601:surgery; D015179:Colorectal Neoplasms / Q000235:genetics / Q000473:pathology* / Q000601:surgery*; D004273:DNA, Neoplasm / Q000032:analysis; D004276:DNA, Satellite / Q000032:analysis; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis
chemical_list: D004273:DNA, Neoplasm; D004276:DNA, Satellite