CXCR4 and cancer: We also screened for expression of several genes associated with cancer cell invasion and metastasis and observed that omeprazole and TCDD decreased expression of MMP-9 and CXCR4 (Figures 3B), and the latter pro-metastatic gene has previous been shown to be repressed by TCDD and other AHR ligands in breast cancer cells [31-34].