CCL2 and breast cancer: MCP-1 is the product of the gene JE, one of the immediate early response genes induced in fibroblasts by PDGF [17,18,19], and several human breast cancer cell lines were found to produce PDGF in vitro [20], suggesting that MCP-1 production by fibroblasts in response to 4T1-sup may be due to PDGF.