In the previous studies using HepG2 for tumor formation [21], HepG2 cells at 106 cells/mouse could not form visible xenografts in nude mice, but its sphere-forming cells at the same amount of sphere forming cells could form xenograft tumors and CD44 expression was found in HepG2 sphere forming cells whereas no CD44 expression in monolayer cultured HepG2 parent cells. This evidence concerns the gene CD44 and neoplasm.