PTEN plays a crucial role in preventing the development of glioblastoma (GBM), a severe and untreatable brain cancer. In GBM, most PTEN deficiencies arise from missense mutations, many of which have not been thoroughly examined. Here, we leveraged genetically modified mice and matched isogenic astrocyte cell cultures to investigate how specific and clinically relevant PTEN mutations (G36E, L42R, C105F, and R173H) behave in the development of GBM driven by EGFR. We report that the tumor-suppressive abilities of these PTEN mutants do not depend on their ability to act as lipid phosphatases but are instead related to their increased presence at the cell membrane. Moreover, these PTEN mutations led to heightened EGFR activity by keeping EGFR within endomembranes longer, affecting its signaling behavior. Through comprehensive studies on global protein phosphorylation and kinase library analyses in cells with the G36E and L42R PTEN mutations, we identified distinct cancer-promoting pathways activated by EGFR, offering new targets for treating GBM with these PTEN alterations.