PTEN and glioblastoma: Interestingly, data from GBM cell lines suggest that high levels of PD-L1 may correlate with mutations in PTEN.52 Unsurprisingly, given its widespread function, meta-analysis of GBM patients with high PD-L1 levels showed a correlation with decreased overall survival lengths, suggesting that this marker may have prognostic value.74 Recent data also suggest that extracellular vesicles that shed from GBM cells can bind PD-1, potentially independent of PD-L1 expression on their surface, to suppress T cell activation.75