Lung Cancer Stem Cells: Current Progress and Future Perspectives

Cancer stem cells (CSCs) have attracted a lot of interest in the field of cancer research in recent years. Lung CSCs share many characteristics with the normal pluripotent stem cells, such as self-renewal and multi-potent abilities. Identification of normal adult lung stem cells and their response to injury has led us to the lung cancer stem cells, partially based on the knowledge that lung CSCs as well as the normal lung stem cells share similar markers and/or location in the airway tree. Several studies have identified CD133, CD44, ALDH (aldehyde dehydrogenase) and ABCG2 (ATP-binding cassette sub-family G member 2) as lung cancer stem cell markers, all of which are validated CSC markers in multiple other cancer types as well. Embryogenesis signaling pathways, such as the hedgehog, wnt and notch pathways has also been implicated as determinants of lung CSC phenotype. With the central role of CSCs in tumor recurrence, metastasis and drug-resistance, targeting CSC markers and/or signaling pathways to eradicate lung cancer and enhance patient outcome is an attractive approach. This review summarizes our current understanding of CSC markers and signaling pathways in lung cancer.