ALDH1A1 and cancer: Secondly, CD24, CD44 and CD133 are specific surface markers that can be expressed by colon cancer stem cells (Choi et al., 2009); ALDH1, OCT4, SOX2 and Nanog are all markers of stemness status of cancer stem cells, which are important for maintaining the nature and drug resistance of cancer stem cells (Liu et al., 2013).