Genetic alterations in DNA diploid, aneuploid and multiploid colorectal carcinomas identified by the crypt isolation technique.

Loss of heterozygosity (LOH) and microsatellite instability (MSI) commonly occur in colorectal carcinomas. However, the role of these genetic alterations in determining DNA ploidy status of tumors (diploid, aneuploid and multiploid) remains unclear. In the present study, we attempted to clarify the relationship between genetic alterations and DNA ploidy status. Crypt isolation coupled with DNA cytometric sorting and polymerase chain reaction assay (17 microsatellite markers) were used to study allelic losses and MSI in 59 colorectal carcinomas (diploid, 15; aneuploid, 10 and multiploid, 34). Of the 15 diploid carcinomas, 6 exhibited MSI in which allelic losses were rarely found. The other 9 diploid tumors mostly exhibited allelic losses, but none displayed MSI status. Whereas allelic losses frequently occurred in the aneuploid carcinomas and the aneuploid populations of multiploid carcinomas, they were rarely detected in the diploid populations of multiploid carcinomas. MSI status was not observed in aneuploid carcinomas nor in either population of multiploid carcinomas. Although multiploid carcinomas genetically resemble aneuploid carcinomas in the expression of the severe LOH phenotype, the genetic alterations seen in the diploid populations of multiploid carcinomas may differ from those of diploid carcinomas. Furthermore, all diploid, aneuploid and both the diploid and aneuploid fractions of the multiploid tumors that were non-MSI exhibited a high rate of LOH, suggesting that LOH is independent of the tumor's ploidy status.