CXCL12 and neoplasm: Inhibition of CXCR4 activation using Plerixafor, an antagonist that blocks CXCL12 binding to CXCR4 was shown to inhibit early bone metastasis growth in a prostate cancer model which was associated with reduced numbers of Ki67 positive tumor cells, suggesting possible induction of tumor cell quiescence, although markers of this were not directly assessed in this study [296].