Table 1 Tenets of the cancer stem cell and clonal evolution models
| Â | Cancer stem cell model | Clonal evolution model |
|---|---|---|
Tumorigenic cells | CSCs | Any cell |
Tumor cell organization | Hierarchical | Stochastic |
Capacity of self-renewal with asymmetric divisions | CSCs can self-renew indefinitely whereas terminally differentiated cells have limited proliferative potential | Not applicable |
Progression | Driven by CSCs, which account for a small subpopulation of the tumor bulk | Driven by the fittest clone under a constellation of selective pressures |
Source of heterogeneity | Aberrant differentiation program and mutations | Epigenetic and genetic aberrations followed by selection |
Type of heterogeneity | Initially perceived as largely phenotypic; however, more recent studies suggested that CSCs may be genetically heterogeneous within a tumor | Genetic and phenotypic heterogeneity |
Source of resistance to therapy | CSCs | Selection of resistant subclones harboring specific genetic or epigenetic aberrations |