Our data unexpectedly show that Twist1 is almost exclusively expressed by the immunosuppressive, mesenchymal-like subpopulation of ECs in mouse GBM tumors (and, to a lesser extent, EMT-acquiring tumor cells in human GBM tumors), suggesting Twist1 as a potential regulator of Endo-MT and vascular niche function. Here, TWIST1 is linked to neoplasm.