In particular, the overexpression of MRP1 (ABCC1), MRP2 (ABCC2), MRP3 (ABCC3), MRP5 (ABCC5), and MRP6 (ABCC6) correlates with a poor prognosis in acute lymphoblastic leukemia in both adults and children [21,22]. This evidence concerns the gene ABCC6 and acute lymphoblastic leukemia.