We observed reduced MMP-9 and MMP-2 activity in CM and tumors of mice downregulated or inhibited for CXCR7, suggesting that CXCR7 positively correlates with MMP(s) secretion in breast cancer cells, or the reduced recruitment of TAMs to the tumor site might be responsible for less secretion of MMPs at the tumor site, thereby reducing the migration of breast cancer. Here, MMP9 is linked to breast cancer.