Colorectal cancer (CRC), the second most common tumor type in the US, is the third leading cause of cancer-related mortality, accounting for nearly 9 percent of ail cancer-related deaths. Accumulation of mutations in multiple critical genes is believed to cause the transformation of a normal mucosal epithelial cell into a cancer cell, Mutations in critical genes, such as APC, KRAS, TP53, MMR family genes, CTNNB1, and SMAD4, have been implicated in colon tumorigenesis. In addition to genetic mutations, epigenetic alterations also play important roles in cancer initiation and development. One subtype of CRC, the CpG island methylator phenotype (CIMP), is characterized by hypermethylation of the CpG islands in the promoter regions of many tumor suppressor and DNA repair genes, resulting in gene inactivation. Other epigenetic alterations in CRC include DNA methylation, his-tone modification, microRNA action, microsatellite instability, and chromosomal instability.
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