CXCR4 and breast cancer: In breast cancer, the SDF-1/CXCR4 and CXCL5/CXCR2 axes recruit Gr-1+CD11b+ myeloid cells, activate MMP, and upregulate TGF-β1, which contributes to metastasis in mouse models injected with a breast cancer cell line (4T1) [124].