Early onset MSI-H colon cancer with MLH1 promoter methylation, is there a genetic predisposition?
BACKGROUND
To investigate the etiology of MLH1 promoter methylation in mismatch repair (MMR) mutation-negative early onset MSI-H colon cancer. As this type of colon cancer is associated with high ages, young patients bearing this type of malignancy are rare and could provide additional insight into the etiology of sporadic MSI-H colon cancer.


METHODS
We studied a set of 46 MSI-H colon tumors cases with MLH1 promoter methylation which was enriched for patients with an age of onset below 50 years (n=13). Tumors were tested for CIMP marker methylation and mutations linked to methylation: BRAF, KRAS, GADD45A and the MLH1 -93G>A polymorphism. When available, normal colon and leukocyte DNA was tested for GADD45A mutations and germline MLH1 methylation. SNP array analysis was performed on a subset of tumors.


RESULTS
We identified two cases (33 and 60 years) with MLH1 germline promoter methylation. BRAF mutations were less frequent in colon cancer patients below 50 years relative to patients above 50 years (p-value: 0.044). CIMP-high was infrequent and related to BRAF mutations in patients below 50 years. In comparison with published controls the G>A polymorphism was associated with our cohort. Although similar distribution of the pathogenic A allele was observed in the patients with an age of onset above and below 50 years, the significance for the association was lost for the group under 50 years. GADD45A sequencing yielded an unclassified variant. Tumors from both age groups showed infrequent copy number changes and loss-of-heterozygosity.


CONCLUSIONS
Somatic or germline GADD45A mutations did not explain sporadic MSI-H colon cancer. Although germline MLH1 methylation was found in two individuals, locus-specific somatic MLH1 hypermethylation explained the majority of sporadic early onset MSI-H colon cancer cases. Our data do not suggest an intrinsic tendency for CpG island hypermethylation in these early onset MSI-H tumors other than through somatic mutation of BRAF.
van Roon
Eddy H J
EH
Department of Pathology, Leiden University Medical Center, Leiden, The Netherlands.
van Puijenbroek
Marjo
M
Middeldorp
Anneke
A
van Eijk
Ronald
R
de Meijer
Emile J
EJ
Erasmus
Dianhdra
D
Wouters
Kim A D
KA
van Engeland
Manon
M
Oosting
Jan
J
Hes
Frederik J
FJ
Tops
Carli M J
CM
van Wezel
Tom
T
Boer
Judith M
JM
Morreau
Hans
H
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D018797:Cell Cycle Proteins / Q000235:genetics; D016009:Chi-Square Distribution; D003110:Colonic Neoplasms / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation; D053843:DNA Mismatch Repair; D004252:DNA Mutational Analysis; D020022:Genetic Predisposition to Disease; D006801:Humans; D019656:Loss of Heterozygosity; D053842:Microsatellite Instability; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D012307:Risk Factors; D018631:ras Proteins / Q000235:genetics; D000097642:GADD45 Proteins
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D048493:Proto-Oncogene Proteins B-raf; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; C439070:GADD45A protein, human; D000097642:GADD45 Proteins; C117307:KRAS protein, human; C501486:MLH1 protein, human; C482119:BRAF protein, human
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