The nonspecificity of histological findings reported for flat adenomas.
Flat adenomas have been reported to be associated with an increased risk of high grade dysplasia and with a genetic predisposition to numerous colonic polyps. Histological findings reported for flat adenomas are dysplastic glands superficial to nondysplastic glands and a thickness of dysplastic mucosa that does not exceed twice that of nondysplastic mucosa. We assessed the specificity of these histological findings with regard to a colonoscopically flat appearance in a series of 127 sequentially accessioned adenomas from 52 patients without adenomatous polyposis coli or inflammatory bowel disease. Thirty-two of the 127 adenomas (25%) from 20 of 52 patients (36%) showed the histological findings outlined above; none of these polyps was grossly flat and none had high grade dysplasia. The predictive values of these histological features for patients younger than 50 years old and for the presence of five or more polyps in a patient were 15% and 25%, respectively. We conclude that the histological findings previously reported for flat adenomas are not specific for that entity and are not uncommonly seen in grossly typical appearing adenomatous polyps. These histological findings also are not associated with high grade dysplasia. They can be seen in polyps from individuals without clinically recognized polyposis, and are relatively poor indicators of young age or increased polyp number, features that could potentially indicate a clinically unrecognized polyposis syndrome. The histological findings in and of themselves thus appear to confer no additional cancer risk to the individual or to the individual's family members over and above that associated with an adenoma.