ABCG2 and acute lymphoblastic leukemia: High expression of ABCB1 and ABCG2 has been associated with reduced chemosensitivity and MDR phenotype in blood cancers such as MM [37,38,39,40,41,42], chronic lymphocytic leukemia (CLL) [43], acute lymphocytic leukemia (ALL), and acute myelogenous leukemia (AML) [44,45,46], as well as solid tumors such as metastatic breast cancer [47].