The dynamics of cancer stem cells

With the formulation of the hierarchical model of tumor cell organization, cancer stem cells came to the forefront of cancer biology. As the only self-renewing tumor cells, they were made responsible for continuous tumor growth and their intrinsic self-protection ability was postulated to underlie cancer therapy resistance and/or recurrence. The concept of migrating cancer stem cells extended the relevance of the hierarchical cancer cell model to issue of cancer progression, with the crucial experimental evidence being provided by the demonstration that epithelial mesenchymal transition can convey stemness. Accordingly, cancer stem cells probably represent a highly dynamic cell population continuously differentiating and being continuously replenished by processes like mesenchymal epithelial transition and epithelial mesenchymal transition, respectively. Consequently, from the point of view of therapeutic targeting, cancer stem cells obviously do not represent a fixed target population any longer. Understanding the dynamic nature of cancer stem cells is thus essential not only for the progress in our understanding of basic cancer biology, but also from the therapeutic perspective.