We had previously reported that CXCL12 could induce in vivo invasion in the MMTV-PyMT transgenic breast cancer model, and that this invasion was dependent on the EGF/CSF-1 paracrine loop between cancer cells and macrophages where CSF-1 is secreted by cancer cells and stimulates macrophages to produce EGF [21]. Here, CXCL12 is linked to breast cancer.