ABCG2 and cancer: We further measured the expression levels of several cancer stemness markers in the scrambled or REEP6-knocked-down SAS cells and found that expression levels of the ATP-binding cassette transporter G2 (ABCG2), cluster of differentiation 166 (CD166) and aldehyde dehydrogenase A1 (ALDH1A1) were significantly decreased in REEP6-knocked-down SAS (Figure 4B).