The effects of the AHR-active pharmaceuticals on CYP1A1 and CYP1B1 expression in MDA-MB-231 cells were similar (Table 1); however, only omeprazole inhibited MDA-MB-231 cell invasion (Figures 1D and 2A) and we therefore selected this widely used proton pump inhibitor for further evaluation as an AHR-active antimetastatic agent in breast cancer. This evidence concerns the gene CYP1B1 and breast cancer.