Table 2.

Comparison of traits of normal Stem Cells and Cancer Stem Cell (CSCs) niches.

Trait	Normal Stem Cells	Cancer Stem Cells
Niche element: mesenchymal cells	Contribute with nutritional and stem-cell-fate factors [82]	Tumors educate the surrounding cells to provide nutrients, although highly resistant to lack of nutrients [83, 84]
Niche element: immune system cells	Modulate local environment for immune protection of SCs (immune suppression = immune-sanctuaries) [85]	Modulate local environment for immune protection of CSCs (immune suppression = immune-sanctuaries) [86]
Niche element: extracellular matrix	The matrix signals to SCs for fate regulation, promoting stemness and physiological maintenance [87]	Cancers cells produce large quantities of metalloproteinases, enzymes that degrade and remodel the ECM, thus promoting invasion and tumor angiogenesis [88]
Niche element: oxygen	Oxygen supply by blood vessels [89, 90]	Highly resistant to lack of oxygen [91], common in specific regions of tumors
Resistance to environmental stress	Highly resistant to cell death by noxious agents [92]	Highly resistant to lack of nutrients. Highly resistant to cell death by chemotherapy agents. Multidrug Resistance (MDR) pumps that extrude toxic compounds ATP-binding cassettes transporters (abc) [93] Quiescence activation through the ability to perceive stress [12, 24]