ABCB1 and acute lymphoblastic leukemia: Notably, many studies have reported that high expression of ABCB1 and/or ABCG2 is associated with MDR [1,2] and poor clinical outcome in patients with metastatic breast cancer (MBC) [5], blood cancers such as acute lymphocytic leukemia (ALL), acute myelogenous leukemia (AML), chronic lymphocytic leukemia (CLL) [6,7,8,9], and multiple myeloma (MM) [10,11,12].