Abstract: The present invention relates to the discovery that renewable stem cell lines can be derived from tumor cells and can be cultured in vitro. Accordingly, the invention provides neural tumor stem cell lines and cells from such cell lines. Because the cell lines retain characteristics of the tumors from which they are derived, the cells can be used in screening methods for identification of potential therapeutic agents and can be used to identify genetic markers which may be predictive for development of such tumors. Finally, such cells can be used to determine an appropriate therapeutic regimen for a patient suffering from a brain tumor. Cells from a patient's brain tumor can be cultured as described herein to create a cell line, and the relative effectiveness of a therapeutic agent against the cells can be tested to determine which agent or combination of agents is most effective in treating the patient's tumor.