Properties of cancer stem cells

Adult stem cells (ASCs) are pluripotent and make up a small percentage of healthy tissue. ASCs are essential for tissue repair, regeneration and growth. ASCs divide into identical stem cells or transiently proliferating cells. The latter cells mature after a number of divisions and become adult differentiating cells. There are different types of cells in cancerous tissue, as in normal, healthy tissue. Most cancer tissues contain three types of cells: (I) cancer stem cells (CSC); (II) cancer initiating cells; and (III) “differentiated”, non-proliferating cancer cells. In the review, the authors present experimental evidences for the presence of CSC, describe cell surface and intracellular markers of CSC. These markers allow for the appropriate identification and isolation of CSC. In addition, the possible location of these cells and theories of their formation are considered. It should be noted, that the theories of CSC originating are in fact theories of neoplasm formation. Many factors and processes may be involved in the formation of CSC. These include: (I) mutations of oncogenes or tumor suppressor genes in spoczynadult differentiated cells; (II) expression of different regulatory RNA types (microRNAs or long non-coding RNAs); processes of epithelial-mesenchymal transition and mesenchymalepithelial transition; (IV) CSC formation from differentiated cancer cells in a consequence of cancer therapy; (V) formation of CSC in conditions of hypoxy and during cell aging. The presented work synthetically characterizes the features, localization and formation of cancer stem cells. Furthermore, the research on these cells is still ongoing and many properties of CSC have not been fully understood.