Xenografting of human tumors has been used to produce samples which are enriched for neoplasia and optimal for subsequent molecular analyses. Molecular studies of xenograft tumors generated from both human colon and pancreatic adenocarcinomas have led to the discovery of important genetic alterations underlying these malignancies (e.g., Smad4, Smad2) (1 ,2 ). Moreover, analysis of pancreatic xenografts helped facilitate the discovery of BCRA2 through identification of homozygous deletions ( 3 ). Furthermore, xenografted tumors have facilitated the discovery of distinctive allelic loss patterns in pancreatic and stomach adenocarcinomas (4 ,5 ). Comparative genomic hybridization analysis of xenografted human gastric cancers has demonstrated consistent DNA copy number changes, including both gains and losses of chromosomal regions (6 ).