The power and the promise of liver cancer stem cell markers.

Recently, there has been growing support for the cancer stem cell (CSC) hypothesis, which states that primary tumors are initiated and maintained by a small subpopulation of cancer cells that possess "stem-like" characteristics. CSCs have been identified in many tumor types, including hepatocellular carcinoma (HCC). The dye, Hoechst 33342, has been used to enrich CSCs into a side population. Alternatively, liver CSCs (LCSCs) can be identified by several cell surface antigens, including CD133, CD90, CD44, EpCAM, and CD13. In this review, we summarized the recent evidence regarding LCSC markers and discussed the origin and function of these markers. LCSC markers are essential to identify and isolate these cells, to develop future therapies targeting CSCs, and to predict prognosis and efficacy of these therapies. However, definite LCSC markers are still controversial, because none of these markers is exclusively expressed by LCSCs in HCC. By combining several positive or negative markers, it may be possible to isolate and identify CSC fractions beyond the ability of each individual assay. By grouping LCSC markers according to their cellular origin, the properties of LCSC markers may be better studied and new markers may be found. Lastly, markers could be used to estimate the number of LCSCs and therefore predict outcomes. From our point of view, selecting HCC tissue samples from patients with different prognoses and detecting expression patterns of marker combinations may be a new method to identify new and unique markers.