Determination of the frequency of loss of heterozygosity in esophageal adenocarcinoma by cell sorting, whole genome amplification and microsatellite polymorphisms

It is well established that the progression to human cancer is characterized by the evolution of clones of cells with accumulated genetic abnormalities. However, technical difficulties limit the ability to study this process in some premalignant and malignant conditions. For example, the progression to esophageal adenocarcinoma in the premalignant condition Barrett's esophagus is characterized by the evolution of genetic and cell cycle abnormalities, but it has been difficult to characterize this process completely because of the small size of biopsies and the relative abundance of genetically normal stromal cells in some esophageal adenocarcinomas and premalignant mucosa. We have combined flow cytometric cell sorting to obtain purified populations of neoplastic cells with whole genome amplification and analysis of microsatellite polymorphisms to determine the frequency of allelic loss on every nonacrocentric autosomal arm in 20 esophageal adenocarcinomas and two high-grade dysplasias. DNA samples of purified flow-sorted aneuploid and corresponding normal tissue were amplified with a degenerate 15mer primer. Aliquots of these reactions were then screened with forty-three highly polymorphic simple sequence repeat markers in PCR-based assays. Allelic losses were observed at polymorphic loci in 38 of the 40 chromosome arms that were analysed and the median fractional allelic loss (FAL) observed in the samples was 0.28. The background allelic loss frequency was estimated at 0.23 with the highest rates of loss observed at 17p (100%), 5q (80%), 9p (64%); 13q (43%), 18q (43%) and 1p (41%). These data represent the first comprehensive allelotype of esophageal adenocarcinoma and show the feasibility of multiloci analyses with small highly purified human biopsy material.