Text: A mutation is a change in the genetic material of cells that may be due to DNA damaging radiations or environmental toxins. Mutations can also be the result of a spontaneous error that occurred during cell division. Cancer is largely due to an accumulation of mutations, involving proto-oncogenes, tumor suppressor genes, DNA repair genes, and apoptosis. For example, colon cancer can begin with a defect in a tumor suppressor gene that allows excessive cell proliferation. The proliferating cells tend to acquire other mutations involving a DNA repair gene, an oncogene, and tumor suppressor genes.