CXCR4 and neoplasm: [18], [19] CXCR4 is also constitutively expressed in several hematopoietic malignancies. [20], [21] The CXCR4/SDF-1 axis regulates the trafficking of HPC to and from the BM, [22] and mediates tumor cell homing to BM in both hematopoietic [23] and solid tumors. [24], [25] Others [26] and we [12] have previously shown that AMD3100 sensitizes AML cells to the cytotoxic effects of chemotherapy presumably through disruption of the protective BM microenvironmental niches.