Cancer stem cells(CSCs)maintain tumor growth by keeping the balance between self-renewal,proliferation and differentiation.Though CSCs occupy a tiny minority,they are the fundamental reason for the formation and recurrence of tumors.CSCs hypothesis suggests that CSCs populate an original tumor,which is resistant to treatments,and repopulate the recurrent tumor after most of the tumor has been removed.CSCs research is one of the most thriving and competitive areas in oncology research because it has the potential to become a predictive factor in radiotherapy.