ABCG2 and B-cell chronic lymphocytic leukemia: Clinical evidence has shown that high expression of ABCB1 and/or ABCG2 is linked with the MDR phenotype in advanced NSCLC [24], metastatic breast cancer [25], acute lymphocytic leukemia (ALL), acute myelogenous leukemia (AML) [26,27,28], chronic lymphocytic leukemia (CLL) [29], and multiple myeloma (MM) [30,31].