In the acute myelocytic leukemia cell line KG-1, MDR1 expression level was the highest (64 copies/103 GAPDH), followed by those of MRP4 (23 copies/103 GAPDH) and MRP1 (15 copies/103 GAPDH; Fig. 1A and C). This evidence concerns the gene ABCC4 and acute myeloid leukemia.