Previous studies have demonstrated that atrazine elicits estrogen action by up-regulating aromatase activity in certain cancer cells with elevated aromatase levels (Fan et al. 2007a, 2007b; Heneweer et al. 2004; Sanderson et al. 2000, 2001) but not by binding to or activating ERα (Connor et al. 1996; Roberge et al. 2004; Tennant 1994a). This evidence concerns the gene ESR1 and cancer.