ABCG2 and breast cancer: The overexpression of ABCB1 and ABCG2 has been linked to the development of acquired drug resistance in numerous types of cancer, such as advanced non-small cell lung cancer [42], breast cancer [43], acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL) [44,45,46], chronic myeloid leukemia (CML) [47], chronic lymphocytic leukemia (CLL) [48], and multiple myeloma (MM) [49,50,51,52,53,54,55].