Taken together, we have established that the inhibition of MDR1 or ABCG2 using either pharmacological inhibitors or RNAi resulted in a significant impairment of the DOX efflux activities in Huh7 and PLC/PRF/5 cells, especially in the EpCAM+–CD133+ subpopulation of these HCC cells. Here, ABCG2 is linked to hepatocellular carcinoma.