CYP2D6 and hepatocellular carcinoma: As measured by dextromethorphan O-demethylation metabolism in human liver microsomes, the intrinsic clearance (Clint) of CYP2D6 increased significantly in HCC patients compared with normal controls (Median: 6.86 μL/min/mg vs 3.49 μL/min/mg, P < 0.01, Fig. 2c).