PD-1 is a receptor that leads to immune system inhibition and interacts with PD-L1, which is expressed on GBM cells.[27] Although promising, PD-1 inhibitors have not yet been shown to improve survival in GBM patients.[27] An increased risk of GBM metastasis in the setting of anti-PD-1 immune checkpoint inhibitors or vaccine-based therapies would be unexpected, as the intention of the immunotherapy is to alert the host immune system to invading GBM cells, especially once they escape the blood-brain barrier. This evidence concerns the gene CD274 and glioblastoma.