ABCG2 and breast cancer: First, we evaluated the ALDH activity, the expression of BCSC genes (Nanog, Sox2 and Oct4) (Supplementary Fig. S6), multiresistance pumps (ABCG2, ABCC1 and ABCB1) (Supplementary Fig. S6) and the BCSC frequency (CD44+CD24+CD49+EPCAM+) (Supplementary Fig. S1c,d) in three human breast cancer cell lines.