Whatever the mechanism through which the AHRR represses AHR activity, low AHRR expression in breast, lung, stomach, cervical, and ovarian cancers (likely mediated by DNA hyper-methylation and gene silencing [160]) has led some to suggest that the AHRR is a “tumor suppressor” [160], a moniker consistent with the description of the AHR as a tumor promoter, at least in some cancers. This evidence concerns the gene AHRR and cancer.