The tumor microenvironment.

Recent advances in stem cell and developmental neurobiology have uncovered new perspectives from which we investigate various forms of cancer. Specifically, the hypothesis at tumors are comprised of a subpopulation of malignant cells similar to stem cells is of great interest to scientists and clinicians and has been dubbed the cancer stem cell hypothesis. The region where this is most relevant is within the brain. Cancer stem cells have been isolated from brain tumors that exhibit characteristics of differentiation and proliferation normally seen only in neural stem cells. These cancer stem cells may be responsible for tumor origin, survival and proliferation. Furthermore, these cells must be considered within their immediate microenvironment when investigating mechanisms of tumorgenesis. Evidence of brain tumor stem cells will be reviewed along with the role of tumor environment as the context within which these cells should be understood.