CXCR4 and glioblastoma: Since both CXCL12 and CXCR4 are highly expressed in normal brain, where CXCL12-CXCR4 axis plays an important role in the CNS development, the involvement of this chemokine-receptor axis in glioblastoma may be considered as an example of tumor cells “hijacking” of physiological processes in CNS [198].