In human breast cancer patients and the murine 4T1 breast cancer model, non-tumor stromal cells were the main source of MCP-1 that promotes lung metastasis [5,6], and granulocyte-macrophage colonystimulating factor (GM-CSF/CSF-2) produced and released by 4T1 cells highly induced MCP-1 production by mouse inflammatory macrophages in vitro [7]. Here, CCL2 is linked to breast cancer.