Investigation of 4-ABP metabolism in vivo in both Cyp1a2(−/−) and Ahr(−/−) mice showed that treatment of mice with 600 or 1200 nmol in two doses at 8 and 15 days of age 4-ABP induced hepatocellular adenoma and liver foci; however, there were no differences found in incidence between Cyp1a2(−/−), Ahr(−/−) and wild-type mice, irrespective of the dose (60). This evidence concerns the gene AHR and hepatocellular adenoma.