MMP9 and breast cancer: CXCR7 is a receptor of CXCL12, which is involvedin breast cancer metastasis via activation of CXCR4.Overexpression of CXCR7 induces tumorigenesis andmetastasis of breast cancer cell lines in vivo(Miao et al.,2007), while its inhibition reduces the expressions of MMP2and MMP9, which are involved in the invasion of cancercells(Gao et al., 2015).