Besides the ABCC2 −24C>T polymorphism (rs717620), other SNPs reportedly associated with the MTX plasma concentration and toxicities in childhood ALL, including rs3740065 in ABCC2, and rs9516519, rs868853 and rs2274407 in ABCC4[14], [15], were examined in this study and showed no significant effects on the MTX plasma concentration. Here, ABCC4 is linked to acute lymphoblastic leukemia.