Flat adenomas in the National Polyp Study: is there increased risk for high-grade dysplasia initially or during surveillance?
OBJECTIVE
The flat adenoma may be a more aggressive pathway in colorectal carcinogenesis. Sessile adenomas from the National Polyp Study cohort were reclassified histopathologically as flat or polypoid and compared with initial and surveillance pathology.


METHODS
A total of 933 sessile adenomas detected during 1980-1990 were reclassified as follows: (1) adenoma thickness (AT): < or =1.3 mm, and (2) adenoma ratio (AR): adenoma thickness <2x normal mucosa thickness. Logistic regression was used to assess whether flat adenomas had an effect on risk for high-grade dysplasia initially, and a Cox proportional hazards model assessed the risk for advanced adenomas at surveillance.


RESULTS
The analysis encompassed 8401 person-years of follow-up evaluation. AT and AR measures of adenoma flatness were 95% concordant. By the AT measure, flat adenomas (n = 474) represented 27% of all baseline adenomas. Flat adenomas were found to be no more likely to exhibit high-grade dysplasia than sessile (polypoid) or pedunculated adenomas, the odds ratio for high-grade dysplasia was 1.91 (95% confidence interval [CI], 0.66-5.47; P = 0.23) for sessile (polypoid) vs. flat adenomas and 1.78 (95% CI, 0.63-5.02; P = 0.28) for pedunculated vs. flat adenomas adjusted for size, villous component, and location, and corrected for correlation of risk within an individual patient. Patients with flat adenomas at initial colonoscopy were not at greater risk for advanced adenomas at surveillance compared with those with polypoid adenomas only, the odds ratio was 0.76 (95% CI, 0.4-1.42; P = .39), adjusted for multiplicity, age, and family history of colorectal cancer.


CONCLUSIONS
Flat adenomas identified in the National Polyp Study cohort at baseline were not associated with a higher risk for high-grade dysplasia initially, or for advanced adenomas at surveillance.
O'brien
Michael J
MJ
Department of Pathology, Boston Medical Center, Boston, Massachusetts 02118, USA. michael.obrien@bmc.org
Winawer
Sidney J
SJ
Zauber
Ann G
AG
Bushey
Marijayne T
MT
Sternberg
Stephen S
SS
Gottlieb
Leonard S
LS
Bond
John H
JH
Waye
Jerome D
JD
Schapiro
Melvin
M
D000236:Adenoma / Q000473:pathology*; D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000473:pathology; D003111:Colonic Polyps / Q000473:pathology*; D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000473:pathology*; D005260:Female; D006801:Humans; D007413:Intestinal Mucosa / Q000473:pathology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011230:Precancerous Conditions / Q000473:pathology*; D016016:Proportional Hazards Models; D016032:Randomized Controlled Trials as Topic; D018570:Risk Assessment