CCL2 and breast carcinoma: CCL2 has long been known to recruit monocytes/macrophages.21 Interestingly, CCL2 can also recruit neutrophils through CCL2-CCR2 signaling in an inflammatory state.22 These previous studies prompted us to investigate whether CCL2 is involved in the recruitment of MHCIIhi neutrophils to promote breast cancer lung metastasis.