Beating Cancer with Cancer Stem Cells is the only way to be cancer free. You must kill the Cancer Stem Cells. The Cancer Stem Cells is a small of the tumor. The following is from Pub Med: Cancer stem cells (CSCs) comprise the subpopulation of tumor bulk and acquire resistant to conventional therapies and are considered as the primary tumor initiator cells. Nowadays, the tumor heterogeneity originated from CSCs, and its progenitors are accepted as a mortifying drawback in front of the cancer therapies. However, escalating knowledge gained from studies investigating the biology of CSCs will open up new frames for targeted therapies and decrease the chance of recurrence of the disease. In this review, the general understanding of CSCs and current studies were discussed briefly. Considering the latest data collected from studies of CSCs, defining the tumor heterogeneity and tumor microenvironment comprehensively will be very important to step up the cancer research. Recently it is considered that there is a small population of cells with stem cell property not only in leukemia but also in solid cancer. These cells show the ability of self-renewal and multi-potential differentiation, and can initiate and maintain a tumor. Since the first prospective identification of cancer stem cells in solid cancers the cancer stem cell hypothesis has reemerged as a research topic of increasing interest. It postulates that solid cancers are organized hierarchically with a small number of cancer stem cells driving tumor growth, repopulation after injury and metastasis. Since the first prospective identification of cancer stem cells in solid cancers the cancer stem cell hypothesis has reemerged as a research topic of increasing interest. It postulates that solid cancers are organized hierarchically with a small number of cancer stem cells driving tumor growth, repopulation after injury and metastasis. They give rise to differentiated progeny, which lack these features. The model predicts that for any therapy to provide cure, all cancer stem cells have to be eliminated while the survival of differentiated progeny is less critical. In this review we discuss recent reports challenging the idea of a unidirectional differentiation of cancer cells. These reports provide evidence supporting the idea that non-stem cancer cells exhibit a remarkable degree of plasticity that allows them to re-acquire cancer stem cell traits, especially in the context of radiation therapy. We summarize conditions under which differentiation is reversed and discuss the current knowledge of the underlying mechanisms.