In particular, hypoxic conditions are known to control the expression of target genes such as VEGF, TGF-β2, MMP-1,2, and 9, human plasminogen activator inhibitor type 1, endothelin-1, and erythropoietin (EPO), influencing angiogenesis, tumor growth, and GBM invasiveness [40,41,42]. Here, EPO is linked to glioblastoma.