The impact of ATRA on gene expression and transporter activity of ABCB1 was analyzed using real-time quantitative polymerase chain reaction (RT-PCR) and the Rh-123 efflux assay in two human AML cell lines, Kasumi-1 (harboring the t(8;21) translocation) and KG-1, as well as in selected populations of leukemic cells isolated from patient samples [75]. The gene discussed is ABCB1; the disease is acute myeloid leukemia.