Causes of microsatellite instability in colorectal tumors: implications for hereditary non-polyposis colorectal cancer screening.
Microsatellite instability (MSI) analysis was performed using a "reference panel" of microsatellite markers in 345 unselected primary colorectal cancers (CRC). Thirty-five (10%) tumors were classified as high MSI (MSI-H). We identified 6 (17%) MSI-H tumors with germline mutations in mismatch repair (MMR) genes (tumors from patients with hereditary non-polyposis colorectal cancer (HNPCC) syndrome) and 29 (83%) MSI-H tumors without germline MMR mutations (sporadic MSI-H tumors). Hypermethylation of the hMLH1 promoter was found in 26/29 (90%) sporadic MSI-H tumors but only in 1/6 (17%) HNPCC tumors (P<.001). Somatic alterations were identified in both MMR genes in HNPCC tumors but mainly in the hMSH2 gene in sporadic MSI-H tumors. LOH at MMR loci was detected in 3/6 (50%) HNPCC tumors and in 4/26 (15%) informative sporadic MSI-H tumors. These results together indicate different mode of inactivation of MMR genes in sporadic MSI-H tumors versus MSI-H tumors in HNPCC patients. We therefore propose that MSI analysis of newly diagnosed primary CRC followed by methylation analysis of hMLH1 promoter in MSI-H tumors and mutational analysis of MMR genes in MSI-H tumors lacking hMLH1 promoter methylation might be an efficient molecular genetic approach for HNPCC screening.
Potocnik
U
U
Laboratory of Molecular Genetics, Institute of Pathology, Medical Faculty, Ljubljana, Slovenia.
Glavac
D
D
Golouh
R
R
Ravnik-Glavac
M
M
D048868:Adaptor Proteins, Signal Transducing; D000368:Aged; D001483:Base Sequence; D002352:Carrier Proteins; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000175:diagnosis / Q000235:genetics*; D019175:DNA Methylation; D004268:DNA-Binding Proteins; D005260:Female; D018095:Germ-Line Mutation; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D008403:Mass Screening; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D008969:Molecular Sequence Data; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000235:genetics; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein