Our understanding of the molecular genetic pathways that lead to the development of colorectal cancer is still evolving, but there appear to be three primary pathways of tumorigenesis. These include:

• Chromosomal instability
• Microsatellite instability
• CpG island hypermethylation, which is an epigenetic change

The chromosomal instability (CIN) molecular pathway is characterized by the consecutive accumulation of chromosomal abnormalities. This pathway is associated with mutations or loss of the APC gene, RAS mutations, mutations or deletions of the deleted-in-colon-cancer (DCC) gene, and/or TP53 mutations. Chromosomal instability is a phenomenon that frequently occurs in left-sided colon cancers.