Glioblastoma (GBM) is the most common malignant primary brain tumor in adults and is one of the most aggressive and deadly forms of cancer. It is difficult for surgeons to fully remove GBM because it often has microscopic "tentacles" that extend from the tumor into healthy brain tissue. GBM is also hard to treat because it creates an immunosuppressive microenvironment that helps the cancer evade immune attack and resist therapy.