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. The gene discussed is CCL2; the disease is breast cancer.