ABCG2 and chronic myelogenous leukemia, BCR-ABL1 positive: Considering that initiating cells in CML arises from a multipotent hematopoietic stem cell (HSC), together with high expression of ABCG2 in human HSCs (Zhou et al., 2001; Scharenberg et al., 2002), overexpression of ABCG2 has been considered to confer drug resistance ability to the CML stem cell population (Brendel et al., 2007).