The similarities and differences between normal tissue stem cells and cancer stem cells (CSCs) have been the source of much contention, with some recent studies calling into question the very existence of CSCs. An examination of the literature indicates, however, that the CSC model rests on firm experimental foundations and that differences in the observed frequencies of CSCs within tumors reflect the various cancer types and hosts used to assay these cells. Studies of stem cells and the differentiation program termed the epithelial-mesenchymal transition (EMT) point to the possible existence of plasticity between stem cells and their more differentiated derivatives. If present, such plasticity would have major implications for the CSC model and for future therapeutic approaches.Excerpt from the full text:
Figure 1: Stem-differentiation hierarchy.
Increased plasticity may be present within cancer populations, enabling bidirectional interconvertibility between CSCs and non-CSCs.Last two sentences of the full text:
However, if non-CSCs can indeed give rise to CSCs, this plasticity would frustrate attempts to cure tumors by eliminating CSCs alone, as therapeutic elimination of CSCs may be followed by their regeneration from residual non-CSCs, allowing tumor regrowth and clinical relapse. We, therefore, suspect that optimal therapeutic regimens will need to incorporate agents that target both CSCs and non-CSCs if truly curative therapies are ever to be achieved.Comment: This article presents a novel model of the "stem-differentiation hierarchy" involving CSCs and non-CSCs. The model includes the possibility that "a dynamic equilibrium may exist between CSCs and non-CSCs within tumors" that "may be shifted in one direction or another by contextual signals within the tumor microenvironment that influence the probability of interconversion between the CSC and non-CSC compartments ...". It's unfortunate that the article isn't openly accessible. If it were OA (with an appropriate Creative Commons License), a copy of the model depicted in Figure 1 could have been included in this post.