Cancer Stem Cells: From an Insight into the Basics to Recent Advances and Therapeutic Targeting

Table 2

Theories suggesting origin of CSCs [11, 12].

Theories	Explanations
CSCs derived from normal stem cells	This theory suggests that for promoting their self-renewal, cancer cells utilize the regulatory pathways of existing stem cells.
	In comparison to mature differentiated cells, the characteristic property of self-renewal provides a longer life span to stem cells.
	Therefore, hypothetically mature cells with limited life span do not undergo multiple mutations which are essential for tumor formation and metastasis.
CSCs derived from progenitor cells	Progenitor cells having the partial ability for self-renewal are more abundant in the adult tissue than the stem cells which form the basis of this hypothesis.
CSCs derived from differentiated cells	It suggests that there is the probability that a tissue which has enough population of differentiated cells could undergo an essential sequence of events for dedifferentiation. These differentiated cells upon induction of epithelial-mesenchymal transition (EMT) acquire stem cell-like phenotype and formation of CSCs.