CXCL12 and plasma cell myeloma: Blockade of the CXCL12–CXCR4/CXCR7 axis has provided encouraging results with respect to immunotherapy of glioblastoma [135], ovarian cancer [136], multiple myeloma [137], acute myeloid leukemia [138], cervical cancer [139], as well as relapsed or refractory multiple myeloma [140].