CXCL12 and glioblastoma: Cathepsin B becomes upregulated in a CXCL12 mediated feedback system with vessel endothelium [71] forming yet another positive mutually reinforcing feedback system active in glioblastoma with negative consequences in that glioblastomas are prodigious synthesizers of CXCL12, a target of treatment in its own right [72, 73].