IntroductionColorectal carcinoma (CRC) is one of the most common malignant tumors worldwide [1-3]. When CRC cells invade vascular system, they may metastasize through circulation, result into that a number of patients were diagnosed only after these metastases had occurred to miss the optimal time window for surgical resection [1-3]. Therefore, early detection of metastatic CRC may improve its prognosis.The invasion and metastases of CRC cells are recently associated with the presence of a subtype of cancer cells, called circulating tumor cells (CTCs) that had dissembled from the primary tumor and subsequently invaded into the blood circulation [4-7]. Cancer stem cells (CSCs) are cancer cells with characteristics of stem cells. CSCs are responsible for tumor initiation, progression, relapse, metastasis and chemo-resistance.Cell surface markers have been generally used for isolation of CSCs by flow cytometry, whereas none of these CSC-markers have been found to be 100% specific, and therefore these markers are actually used to enrich CSCs from a certain tumor. Hence, most characterized “CSCs” are actually CSC-like cells [8-12]. The gold standard to identify CSCs or CSC-like cells is by tumor sphere formation and by tumor formation in serial adoptive transplantation. CD133 has be-en used to isolate CTCs or CSCs for various cancers, including CRC [8-12]. However, CD133 appears to be lack of cancer specificity and to poorly characterize CSCs in many cases [13]. ALDH1 is a detoxifying enzyme responsible for the oxidation of intracellular aldehydes to be used in identification of stem/progenitor cells or CSCs [14-19]. However, recent evidence suggests the presence of aldefluor-positive cells in other populations, e.g. proliferating pancreatic beta cells [20, 21]. CD44 is another CSC maker that has been used in CRC [22-24]. However, it