Cancer stem cells and survival pathways

Gliomas and medulloblastomas are the most frequent malignant brain tumors in adult and children respectively. Although both tumors arise in the CNS, there is a significant difference in their therapeutic response, resulting in medulloblastomas as being relatively curable, while glioblastomas are basically incurable. During the last decade several reports have demonstrated the existence of cancer stem cells in brain tumors, their location and their response to treatment. We have recently described the therapeutic response of medulloblastomas to radiation in their native microenvironment, describing how p53 and PI3K signaling pathway leads to nestin-expressing cells in the perivascular stem cell niche evading cell death while the tumor-bulk succumbs to apoptosis 1. It remains to be determined whether this mechanism of tumor resistance applies to the more complex stem-cell niche and tumor bulk of gliomas.