Abstract
Recently, there is an increasing evidence supporting the theory of cancer stem cells not only in leukemia but also in solid cancer. To date, the existence of cancer stem cells has been proven in acute and chronic myeloid leukemia, in breast cancer, in brain tumors, in lung cancer and gastrointestinal tumors. This review is focusing on the recent discovery of stem cells in leukemia, human brain tumors and breast cancer. A small population of cells in the tumor (less than 1%) shows the potential to give rise to the tumor and its growth. These cells have a substantial characteristic of stem cells--ability for self-renewal without loss of proliferation capacity with each cell division. Furthermore they are immortal, rather resistant to treatment and express typical markers of stem cells. The origin of these resident cancer stem cells is not clear. Whether the cancer stem cells originate from normal stem cells in consequence of genetic and epigenetic changes and/or redifferentiation from somatic tumor cells to the stem-like cells remains to be investigated. We propose the idea of the relation between normal tissue stem cells and cancer stem cells and their populations--progenitor cells. Based on this we highlight one of the major characteristic of stem cell--plasticity, which is equally important in the physiological regeneration process as well as carcinogenesis. Furthermore, we consider the microenvironment as a limiting factor for tumor genesis in AML, breast cancer and brain tumors. Thus the biological properties of cancer stem cells are just beginning to be revealed, the continuation of these studies should lead to the development of cancer stem cells target therapies for cancer treatment.
Highlights
Stem cells are characterized by their capability for unlimited proliferation and their ability to self-renew by symmetric or asymmetric division
The ability of self-renewal is one of the limiting carcinogenesis factors. This was acknowledged in studies performed by a couple of laboratories. They identified small cell populations that were responsible for tumor formation and their experiments clearly showed the existence of cancer stem cells for leukemia, brain tumors and breast tumors [26]
The first steps in proving the capability of hematopoietic stem cells in initiating the formation of acute myeloid leukemia (AML) were shown in experiments taken by Dick et al It was demonstrated that in AML, only a small subpopulation of leukemic cells are capable of initiating leukemia in SCDI mice [5]
Summary
A small population of cells in the tumor (less than 1 %) shows the potential to give rise to the tumor and its growth These cells have a substantial characteristic of stem cells – ability for self-renewal without loss of proliferation capacity with each cell division. They are immortal, rather resistant to treatment and express typical markers of stem cells. We propose the idea of the relation between normal tissue stem cells and cancer stem cells and their populations – progenitor cells Based on this we highlight one of the major characteristic of stem cell – plasticity, which is important in the physiological regeneration process as well as carcinogenesis. The biological properties of cancer stem cells are just beginning to be revealed, the continuation of these studies should lead to the development of cancer stem cells target therapies for cancer treatment
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