KRAS and astrocytoma (excluding glioblastoma): Mice with abrogation of Rb-TS promoted grade II astrocytomas without any solid tumor mass within 6 months, but when layered with Kras activation mutant (KRASG12D), developed grade III and grade IV high grade astrocytomas, with 4-6 months of latency (Mice with genotype KRASG12D; GFAP-CreERT2 will be referred as R and TgGZT121; KRASG12D; GFAP-CreERT2 as TR) (9).