Cancer Stem Cells (CSCs) in Lung Cancer

The cancer stem cell model for tumor progression is the first model of its type to suggest that only one subpopulation of cancer cells is capable of proliferating indefinitely. These cells resemble normal stem cells in their capacity for self-renewal and multi-potential differentiation, and can both initiate and maintain tumors. The prevailing names for these cells are “cancer stem cells (CSCs)” and “cancer initiating cells (CICs).” The CSC model implies a hierarchical organization within the tumor in which a limited number of CSCs represents the apex of the hierarchy. CSCs are chemo-resistant, radio-resistant, and quiescent, and have been shown to cause both metastasis and relapse. CSCs were first described in patients with acute myeloid leukemia (AML) by Dick et al. (Lapidot et al., 1994). As to be expected from leukemia stem cells, these CSCs exhibited the properties of self-renewal, proliferation and multipotency. The frequency of these leukemiainitiating cells in the peripheral blood of those AML patients was one engraftment unit in 250,000 cells. Dick et al. identified the leukemia-initiating cells as CD34+CD38-. In the years since, CSCs have been identified in cancers of the breast(Al-Hajj et al., 2003), brain (Singh et al., 2003) and prostate, pancreas and lung (Eramo et al., 2008). In this chapter we review CSCs in lung cancer.