CCL2 and cancer: Untreated osteoblasts in vitro and osteoblasts lining the bone marrow in vivo release a variety of cancer promoting cytokines such as interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1) [4], [41], both of which have also been shown to promote cancer cell migration and invasion [4], [42], [43].