CXCR4 and plasma cell myeloma: After the first and/or the second hit, myeloma cells up-regulate the expression of surface adhesion molecules including CXCR4, E-cadherin, Integrin α4β1 (also called very late antigen-4, VLA-4), leukocyte function-associated antigen-1 (LFA-1), vascular cell adhesion molecule 1 (VCAM-1), intracellular adhesion molecule-1 (ICAM-1), etc. These changes in surface adhesion molecules allow the myeloma cells to home to the bone marrow microenvironment [76].