CXCR4 and plasma cell myeloma: Due to its wide expression on several cell lineages, CXCR4 inhibition has been tested for different purposes and the CXCR4 inhibitor (Plerixafor) has been clinically approved for the mobilization of CD34+ hematopoietic stem cells for autologous transplantation in patients with lymphoma or multiple myeloma (19).