Abstract
In this chapter, we will learn that compared to normal cells, cancer cells show epigenetic drifts. These are genome-wide changes in DNA methylation, histone modifications and 3D chromatin structure representing epimutations. Moreover, many malignant tumors reactivate programs of fetal development indicating that tumorigenesis is associated with epigenetic reprogramming. The mechanistic bases of cancer epigenomics are specific genetic, environmental and metabolic stimuli that disrupt the homeostatic balance of chromatin, which then either becomes very restrictive or permissive. Very most types of cancers display a clear epigenetic contribution to the different hallmarks of cancer suggesting that epigenetic modulators, modifiers and mediators form an additional classification system for cancer genes.