Abstract
Emerging evidence suggests that cancer stem cells account for the initiation and progression of cancer. While many types of cancer stem cells with specific markers have been isolated and identified, a variety of differences among them began to be appreciated. Cancer stem cells are hierarchical populations that consist of precancerous stem cells, primary cancer stem cells, migrating cancer stem cells and chemoradioresistant cancer stem cells, playing different roles in cancer initiation and progression. Here we propose a new concept "horizontal hierarchy of cancer stem cells" to distinguish them from vertical hierarchy cancer stem cells, cancer transient-amplifying cells and cancer differentiated cells, and summarize our current understanding of these subsets of cancer stem cells with the aim to open up novel therapeutic strategies for cancer based on this understanding.
Highlights
Cancer is a kind of abnormal tissue that develops the ability of unlimited growth and the resistance to various survival stresses
Zhang et al [94] discovered that in three-dimensional culture, epithelial growth factor receptor tyrosine kinase inhibitor erlotinib inhibited the motility of inflammatory breast cancer (IBC) cell line SUM149 and its invasion in matrigel, accompanied with increased expression of E-cadherin and reduced expression of vimentin and b-catenin
This study suggests that erlotinib reversed epithelial to mesenchymal transition (EMT) of IBC to inhibit metastasis
Summary
Cancer is a kind of abnormal tissue that develops the ability of unlimited growth and the resistance to various survival stresses. Zhang et al [94] discovered that in three-dimensional culture, epithelial growth factor receptor tyrosine kinase inhibitor erlotinib inhibited the motility of inflammatory breast cancer (IBC) cell line SUM149 and its invasion in matrigel, accompanied with increased expression of E-cadherin and reduced expression of vimentin and b-catenin They transplanted SUM149 cells into athymic nude mice and demonstrated that erlotinib inhibited the growth of tumor and lung metastasis by regulating the expression of E-cadherin and vimentin. Precancerous stem cells may be originated from normal stem cells, progenitors which acquire unlimited self-renewal, or differentiated mature cells after reprogramming They may exist in precancerous lesions and are able to transform into primary cancer stem cells or benign tumor stem cells depending on the microenvironment. Whether chemoradioresistant cancer stem cells can transform into migrating cancer stem cells is still not known
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