CXCL12 and central nervous system cancer: In agreement with a role of the CXCL12/CXCR4 axis in promoting MC migration into the tumors, mMCP-6 positive MCs in both Ntv-a Arf−/− and Gtv-a Arf−/− mouse gliomas were frequently (with an average of 90%) CXCR4 positive (Figure 5A–C).