Cancer stem cells are the rare cells within tumors with the power to self-renew and provides rise to the phenotypically diverse tumor cell population to drive tumorigenesis. Only a little subset of cancer cells is capable of in depth proliferation. The frequency of those during a tumor is very variable. Cancer stem cells may have different sensitivities to radiation or chemotherapy. Review articles are the summary of current state of understanding on a specific research topic. review comes within the sort of systematic reviews and literature reviews and are a sort of secondary literature. Systematic reviews determine an objective list of criteria, and find all previously published original research papers that meet the standards . They then compare the results presented in these papers. Literature reviews, against this , provide a summary of what the authors believe are the simplest and most relevant prior publications.