In one series of experiments, genetic and stereotactic methods indicated that gliomas formed by combined loss of NF1 and TP53 and/or PTEN were restricted to neural stem/progenitor cells and were not initiated from cell types in the cortex or cerebellum [12], while in another experimental system, similar NF1/TP53 deleted gliomas appeared to arise from non-stem cells [13]. The gene discussed is PTEN; the disease is central nervous system cancer.