CX3CL1 and neoplasm: Although the identity of tumor-derived cytokines/chemokines that modulate the recruitment of microglia remains unclear, several common chemokines and receptors have been found to be up-regulated in brain tumors, including monocyte chemoattractant protein-1 (MCP-1), granulocyte/macrophage-colony stimulating factor (GM-CSF), fractalkine (CX3CL1), and CCL [67,68].