CCL2 and breast cancer: CCL2 is the product of the gene JE, one of the immediate early response genes induced in fibroblasts by PDGFs [167], and several human BC cell types have been shown to produce PDGFs [168], leading us to test the hypothesis that activation of fibroblasts by 4T1 cell-derived PDGFs contributes to overall CCL2 production by 4T1 tumors.