CYP2B6 and hepatocellular carcinoma: Finally, we validated the functional activity of CAR in human HCC tissues by measuring the relative gene expression of several functional downstream markers of active CAR including CYP2A6, CYP2B6, and UGT1A11,2 (Fig. 1O) and found a significant down-regulation of CYP2B6 and UGT1A1 (P < 0.05) gene expression in tumor tissues, indicating significantly reduced CAR activity in human HCC.