Stem cells and brain cancer

Cancer stem cells have been identified in human tumors. Initial findings in human leukemia suggested that tumors are organized hierarchically with a tumor-initiating rare cell population on the top of the hierarchy being responsible for tumor growth and metastasis. In the last decade, these findings have been extended to several human cancers, and although several convincing results have been published, it is still controversial if cancer stem cells represent a rare, immutable subpopulation perpetuating in the tumor or rather a functional state that many tumor cells can acquire. Since the term cancer stem cells seems to imply that tumor cells derive from normal stem cells of the same tissue, the definition as tumor - initiating cells found a better consensus. The ability of being tumor - initiating cells is the most important feature of these cells, and this is evaluated by the formation of phenocopies of the original tumor in animal models.