**1.1 Origin of CSC**

A number of theories have been proposed for the generation of these CSCs. (1)CSC can originate from genetic/ epigenetic alteration of normal stem cells or from the progenitor cells. (2) They can be derived from somatic tumor cells by de differentiation or reprogramming into a stem- like cell (Visvader and Lindeman, 2008). (3) And recently it has been suggested that CSC can be generated from non-CSC through production secretary molecules (Iliopoulos *et al.*, 2011).
