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Tumorigenesis and neoplastic progression
Distinct Profiles of Epigenetic Evolution between Colorectal Cancers with and without Metastasis

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Liver metastasis is a fatal step in the progression of colorectal cancer (CRC); however, the epigenetic evolution of this process is largely unknown. To decipher the epigenetic alterations during the development of liver metastasis, the DNA methylation status of 12 genes, including 5 classical CpG island methylator phenotype (CIMP) markers, was analyzed in 62 liver metastases and in 78 primary CRCs (53 stage I–III; 25 stage IV). Genome-wide methylation analysis was also performed in stage I–III CRCs and in paired primary and liver metastatic cancers. Methylation frequencies of MGMT and TIMP3 increased progressively from stage I–III CRCs to liver metastasis (P = 0.043 and P = 0.028, respectively). The CIMP-positive cases showed significantly earlier recurrence of disease than did CIMP-negative cases with liver metastasis (P = 0.030), whereas no such difference was found in stage I–III CRCs. Genome-wide analysis revealed that more genes were methylated in stage I–III CRCs than in paired stage IV samples (P = 0.008). Hierarchical cluster analysis showed that stage I–III CRCs and stage IV CRCs were clustered into two distinct subgroups, whereas most paired primary and metastatic cancers showed similar methylation profiles. This analysis revealed distinct methylation profiles between stage I–III CRCs and stage IV CRCs, which may reflect differences in epigenetic evolution during progression of the disease. In addition, most methylation status in stage IV CRCs seems to be established before metastasis.

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Supported by grants-in-aid for cancer research from the Ministry of Health, Labor, and Welfare; by a grant from the Japan Society for the Promotion of Science, the Japanese Society of Gastroenterology, and the Sagawa Foundation for Promotion of Cancer Research; and by a Japan-China Sasakawa Medical Fellowship (H.J.).

None of the authors disclosed any relevant financial relationships.

Supplemental material for this article can be found at http://ajp.amjpathol.org or at doi:10.1016/j.ajpath.2010.12.045.