However, even if ABCB1 is regulated in human hepatocytes or hepatoma cell lines treated with PXR ligands, there are data suggesting a limited effect on hepatic expression of ABCB1 in patients treated with carbamazepine, suggesting that response to this PXR inducer is tissue specific (Dürr et al., 2000; Oscarson et al., 2006). This evidence concerns the gene ABCB1 and hepatocellular carcinoma.