CXCL12 and glioblastoma: CXCL12–CXCR4/R7 system plays a central role in tumor development and tumor cell proliferation, mainly acting via an autocrine/paracrine mechanism, and contributes to the dissemination and invasiveness of several human cancers, including pancreatic, colon, ovarian, prostate, breast, and renal carcinomas, lymphoma, melanoma, neuroblastoma and GBM (Zlotnik, 2006; Barbieri et al., 2010; Lippitz, 2013; Singh et al., 2013).