Fig. 1

The Hierarchical Cancer Stem Model. In this simplified model, the standard somatic stem cells, give rise to healthy cells and also maintain their stem cell pool. In the epithelial cancers the somatic stem cells can give rise to the hierarchical cancer stem cells that retains much of the properties of the somatic stem cell, but gives rise to cancer cells. In some malignancies, cells with stem-like qualities can arise from within the tumour cell pool in a stochastic model