Cancer stem cells: cell culture, markers, and targets for new therapies.

A cancer stem cell (CSC) is defined as an undifferentiated cell with the ability to self-renew, differentiate to multiple lineages and initiate tumors that mimic the parent tumor. In this review, we focus on glioblastomas, describing recent progress and problems in characterizing these cells. There have been advances in CSC culture, but tumor cell heterogeneity has made purification of CSCs difficult. Indeed, it may be that CSCs significantly vary from tumor to tumor. We also discuss the proposal that CSCs are resistant to radiotherapy and chemotherapy and play a major role in repopulating tumors following treatment. To overcome their resistance to conventional therapies, we may be able to use our extensive knowledge of the signaling pathways essential for stem cells during development. These pathways have potential as targets for new glioblastoma therapies. Hence, although there is an ongoing debate on the nature of CSCs, the theory continues to suggest new ideas for both the lab and the clinic.