CXCR2 and breast carcinoma: Moreover, in a mouse model of breast cancer lung metastasis, MSCs that were pre-conditioned with TNFα and co-injected with tumor cells were shown to recruit CXCR2+ neutrophils by secreting CXCR2 ligands (CXCL1, CXCL2, and CXCL5), resulting in enhanced lung metastasis (34).