In animal models of breast cancer, stable expression of CCL2 shRNAs in breast tumor xenografts or treatment of primary tumors with CCL2 neutralizing antibodies leads to decreased primary tumor growth and systemic metastasis, correlating with decreased recruitment of M2 polarized macrophages to tissues (Fujimoto et al., 2009; Hembruff et al., 2010; Qian et al., 2011). Here, CCL2 is linked to breast cancer.