CXCR4 and plasma cell myeloma: Extramedullary myeloma cells generally downregulate chemokine receptors (e.g., CXCR4, CCR1, CCR2) and adhesion molecules (e.g., CD56, CD177, VLA-4), while upregulating migration molecules (e.g., CD44, CD81, nestin) (Figure 1) [69].