Importantly, the SVZ of the three Type 2 cases with near-2N/Pten/chr19-normal tumor cells was free of high-grade gliomas, and some cases, except for increased numbers of Olig2+ cells, resembled a normal SVZ stem-cell niche (Fig. 3e and Supplementary Fig. 5f)19. This evidence concerns the gene PTEN and central nervous system cancer.