Biology of brain tumor stem cells.
of Neurosurgical Focus, highlights how tumor-initiating brain tumor stem cells (BTSC) rely upon many of the same cell cycle regulatory mechanisms, developmental programs, and germinal niches as normal neural stem cells. Functional similarities include multipotency, self-renewal, and migratory capacity. The shared properties of these normal and abnormal cells suggest a unified lineage, although the directionality of this relationship remains unknown. One persistent challenge is our inability to recognize these cells. To date, there exists no marker that specifically identifies normal neural stem cells. Similarly, although CD133 has been popularized as a BTSC marker, CD133-negative BTSCs are also capable of brain tumor initiation. We agree that further characterization of BTSCs is of tremendous interest and may facilitate targeting of potent cellular populations in brain tumors. Any discussion, however, of the implications (if any) of brain tumor therapy for normal neural stem and progenitor cells would first require evidence demonstrating the functional significance of these cells in humans. Moreover, exploiting the therapeutic potential of BTSCs will require additional insight into the fundamental mechanisms governing normal neural stem and progenitor cells, a phenotypically diverse population that varies in spatial and temporal distribution throughout postnatal life. Attention should also be paid to species-specific properties, as findings do not all necessarily translate directly to the human system.