Objective Somatic stem cells(SSCs) have the capability of self-renewal,and reside in a microenvironment named "niche" after their generation,in which the features of "stem cells" are kept.Cancer stem cells(CSCs) are capable of initiating and sustaining the tumor growth,with features of self-renewal,too.There are many resemblances between CSCs and SSCs,including the self-renewal regulatory pathways: Bmi1,WNT,Hedgehog,etc.The function of self-renewal is strictly controlled in normal stem cells,but mutations in CSCs make it loss of control,an important event during tumorigenesis initiated by CSCs.