DNA Methylation tests for the presence and development of cancer. Too little methylation of DNA, hypomethylation, is a tumor marker for several types of cancer, including breast cancer. Too much methylation of DNA, hypermethylation, is a tumor marker for several types of cancer. Sensitive methylation measurement techniques are being developed that can identify tissue that is precancerous. Because methylation can be reversed chemically with demethylation drugs, early detection could mean early and effective treatment.