CXCR4 and plasma cell myeloma: Plerixafor, a CXCR4 antagonist approved to enhance the mobilization and collection of hematopoietic stem cells for autologous transplantation in patients with Non-Hodgkin’s lymphoma and multiple myeloma, is under investigation to be applied for the mobilization of leukemic stem cells, in order to improve their elimination from the bloodstream through chemotherapy.