Epigenetic abnormalities can lead to cancer as often as genetic aberrations, if not more frequently. This, we are discovering, is even true for cancers that were classically viewed as purely mutation-driven, such as those caused by cigarette smoking. Moreover, some of the genes frequently mutated in cancers, for example BRCA1 in breast and ovarian cancers or MLL in leukemia, encode for epigenetic enzymes, thus bringing epigenetics into play in what started as a genetic disease.