AHR and breast cancer: From the studies in breast cancer, Safe found two classes of selective AhR modulators: Alternate-substituted (1,3,6,8- and 2,4,6,8-) alkyl polychlorinated dibenzofurans (PCDFs) and substituted diindolylmethanes (DIMs), compared to TCDD, these compounds are relatively non-toxic and inhibit ER-positive and ER-negative mammary tumor growth, but do not induce AhR-mediated toxic responses induced by TCDD [19].