CCL2 and neoplasm: Numerous factors, known to be present in the bone-tumor microenvironment, have been shown to induce MCP-1 secretion and gene expression including MCP-1 itself [39], TGF-β [40,41], tumor necrosis factor-alpha (TNF-α) [42], parathyroid hormone related peptide (PTHrP) [39] and various interleukins [43,44].