Figure 2.

Schematic representation of the normal stem cells and cancer stem cells. (A) Totipotent stem cells, such as zygotes, can generate all the types of cells that form total individual organisms. Pluripotent stem cells can give rise to all three germ cell layers. The inner cell mass of blastocysts furnishes embryonic stem cells, and the reprogramming of terminally differentiated cells supplies pluripotent stem cells. Multipotent stem cells can differentiate into organ-specific cell lineages. Adult tissue-specific stem cells such as intestinal stem cells, hematopoietic stem cells, neural stem cells, and mesenchymal stem cells give rise to terminally differentiated cells to maintain tissue homeostasis. (B) Cancer stem cells (CSCs) are cancer cells that possess stem cell-like properties. CSCs have both self-renewal ability and differentiation potential into non-CSCs, which have low tumorigenicity. (C) CSCs have resistance against conventional chemotherapy and radiotherapy because of multiple mechanisms. As a result of this resistance, CSCs survive such treatments and cause tumor recurrence.