CD133 negative cancer stem cells in glioblastoma.

Glioblastomas (GBM) are paradigmatic for the investigation of cancer stem cells (CSC) in solid tumors. Recently, the discovery of CD133- CSC in addition to CD133+ CSC has substantially added to our understanding of the complexity of GBM CSC. This review gives an overview on our current knowledge on CD133- cells in GBM and describes five different hypothesizes on the nature of CD133- cells in GBM. In addition, we summarize the current knowledge on tumorigenic CD133- CSC, list available markers, describe the current controversies on the origin of CD133- CSC, and discuss how the heterogeneity of CSC may correspond to the molecular heterogeneity of GBM.