The stimulus for this colonisation by ECs is likely to be SDF-1 via its receptor CXCR4 (Orimo et al, 2005) and/or its receptor CXCR7, which is highly expressed in tumour-associated blood vessels including those in GBM (Miao et al, 2007; Liu et al, 2010). Here, CXCL12 is linked to glioblastoma.