Some authors have reported significant correlations between the overexpression of P-gp or MRP-1 and a poor treatment response in solid tumors and some leukemias (Brinkhuis et al., 2002; Diestra et al., 2003; Larkin et al., 2004; Damiani et al., 2006), and a prognostic significance for BCRP overexpression in specific forms of leukemia (Larkin et al., 2004). This evidence concerns the gene ABCC1 and leukemia.