Hypermethylation of multiple genes in pancreatic adenocarcinoma

Hypermethylation of CpG islands is a common mechanism by which tumor suppre ssor genes are inactivated. We studied 45 pancreatic carcinomas and 14 norm al pancreata for aberrant DNA methylation of CpG islands of multiple genes and clones using methylation-specific PCR (MSP) and bisulfite-modified sequ encing. Using MSP, we detected aberrant methylation of at least one locus i n 60% of carcinomas. The genes analyzed included RAR beta (methylated in 20 %), p16 (18%), CACNA1G (16%), TIMP-3 (11%), Ecad (7%), THBS1 (7%), hMLH1 (4 %), DAP kinase (2%), and MGMT (0%). In addition, aberrant methylation was f ound in three CpG islands MINT31, -1, and -2 in 38, 38, and 14% of carcinom as, respectively. Hypermethylation was largely confined to the carcinomas w ith only three Loci (E-cad, DAP kinase, and MINT) harboring methylation in some normal pancreata (36, 21, and 14%, respectively). Simultaneous methyla tion of at least four loci was observed in 5 of 36 (14%) pancreatic adenoca rcinomas. We defined this subgroup of pancreatic adenocarcinomas as "CpG Is land-methylator-phenotype positive (CIMP+)" Two of four carcinomas with mic rosatellite instability harbored promoter hypermethylation of hMLH1, and bo th cases were CIMP+. Thus, we conclude that many pancreatic carcinomas hype rmethylate a small percentage of genes, whereas a subset displays a CIMP+ p henotype.