[Cancer stem cells in pediatric brain tumors]

Cancers are formed by heterogeneous cell types from immature highly proliferative cells to lineage-committed differentiated cells. Transplantation studies have suggested the existence of "cancer stem cells", individual cells capable of producing an entire tumor. Recent advances in stem cell research have allowed for the demonstration of the existence of cancer stem cells in acute myeloid leukemia, breast cancer, and, most recently, in pediatric brain tumors. Each of these has some similarities with the normal stem cells in the corresponding organs. For example, leukemia stem cells express some, but not all, markers of hematopoietic stem cells. Regarding pediatric brain tumors, putative cancer stem cells were identified from medulloblastoma and also from glioma. These tumor-derived cells self-renew under clonal conditions, and differentiate into neurons and glia as well as into abnormal cells with mixed phenotypes. Interestingly, the tumor stem/progenitors, enriched in culture, maintained proliferation after 4 weeks from transplantation into neonatal rat brain. In this review, we discuss the difference as well as the similarity between tumor and normal stem cells, and also the possible clinical implication of cancer stem cells.