Microsatellite Instability is Associated with the Macroscopic Configuration of Neoplasms in Patients with Multiple Colorectal Adenomas

Background: The management of patients with multiple colorectal adenomas, 10-100 in number, is often troublesome clinically. To establish the reasonable management of such cases, genetic backgrounds should be made clear. Methods: For a total of 19 adenomas and four carcinomas from four patients with multiple colorectal adenomas, we analyzed genetic instability at four selected microsatellite loci and screened exon 1-4 of the APC gene with special reference to macroscopic configurations of adenomas and carcinomas. Results: RER-positive phenotypes were detected in none of 13 protruded type adenomas, two (33%) out of six superficial elevated type adenomas and two (50%) out of four carcinomas. We detected no mutation of exon 1-4 of the APC gene in any sample. In patients with multiple colorectral adenomas, the proportion of superficial elevated type adenomas exhibiting genetic instability was significantly higher than that of protruded type adenomas. Conclusions: The results suggested that RER-positive phenotype was an early event in tumorigenesis through superficial elevated type adenomas.