Researchers have proposed that an on and off epigenetic switch could be a common mechanism behind the development of different types of cancer. Epigenetics is the phenomena whereby genetically identical cells express their genes differently resulting in different physical traits. The current paradigm states that cancer develops from environmental and genetic changes to cancer progenitor cells. These changes are the result of mutations exposure to toxic substances or hormonal imbalances. Cancer progression is extremely complex however. It also is well known that new mutations and the activation of more cancer causing genes occur throughout the development and progression of cancer.