 Disruption of asymmetric cell division leads to aberrant self-renewal and impairs differentiation, and could therefore constitute an early step in the tumorogenic transformation of stem and progenitor cells.In normal non-tumor stem cells, a number of genes have been described which are responsible for pluripotency, such as Bmi-1, Wnt and Notch.These genes have been discovered also in the case of cancer stem cells, and shows that their aberrant expression is essential for the formation of tumor cell mass.