In addition to the multidrug-resistant efflux pump gene ABCG2, which was responsible for effluxing Hoechst 33342, the sorted SP cells also expressed higher levels of not only CD133, a putative cell surface marker for hepatoma stem cells isolation [19], but also other stemness genes such as SMO, β-catenin Oct-4 as well as clonogenicity than those in non-SP cells. Here, ABCG2 is linked to hepatocellular carcinoma.