Carcinogenesis, also called oncogenesis or tumorigenesis, is that the formation of cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abnormal cellular division. Cell division is a physiological process that occurs in almost all tissues and under a variety of circumstances. Normally the balance between proliferation and programmed cell death, in the form of apoptosis, is maintained to ensure the integrity of tissues and organs. According to the prevailing accepted theory of carcinogenesis, the somatic mutation theory, mutations in DNA, and epimutations that cause cancer disrupt these orderly processes by disrupting the programming regulating the processes, upsetting the traditional balance between proliferation and necrobiosis. This leads to uncontrolled cell division and therefore the evolution of these cells by survival within the body. Only certain mutations lead to cancer whereas the majority of mutations do not.