We've long known that cancer is caused by genetic abnormalities, but only recently have researchers discovered that epigenetic abnormalities can cause it, too. Epigenetic abnormalities occur in the process of DNA methylation. The creation of some oncogenes, responsible for the uncontrolled cell growth in cancer, begins when something goes wrong in the DNA methylation process. Hypermethylation occurs, which means that there's an overabundance of methyl tags attached to the C base. This abnormal message tells the cells to replicate much faster than normal. Some anti-oncogenes may also be the result of a problem that occurs during DNA methylation, in which the tags turn off the genes that would typically suppress the growth of tumors.
Researchers aren't completely sure why or how the DNA methylation process goes wrong. One theory is that our epigenes simply become abnormal over our lifetime as we experience tissue damage, either from aging or from environmental factors. An older person has more epigenetic damage than a younger person. When our tissue is damaged, our cells must divide and replicate in order to repair and replace it. Over time, the cells lose their ability to perform this function as accurately as they used to. The more frequently they have to divide, the more likely it is for something to go wrong. After a certain number of divisions (exactly how many is unknown), some epigenes appear to stop tagging the genes correctly.