PTEN and glioblastoma: Novel technologies such as CRISPR/Cas9 have also increased the flexibility and granularity of GEMMS.102 CRISPR/Cas9 has been used to create a variety of GEMMS with single and multiple gene mutations.103,104 This is highlighted by Oldrini et al. who utilized CRISPR/Cas9 to knock out either a single tumor suppressor gene, PTCH1, or multiple genes TRP53, PTEN, NF1, to create models of medulloblastoma and GBM, respectively.103 Exciting applications of this technology include in vivo CRISPR/Cas9 screens.