This study reports that rat mammary tumors induced with the AhR-agonist 7,12-dimethyl-benzo(a)anthracene (DMBA) [48] had augmented CpG methylation of the Brca-1 gene; higher expression of Ahr, Cyp1b, and proliferation markers (Cdk4, Ccnd1); and diminished expression of BRCA-1 and ERα. The gene discussed is CDK4; the disease is breast cancer.