Stem cell plasticity and carcinogenesis

Presently, there is more and more talk about tumors being a disease connected with stem cells. Both stem cells and tumor cells have many similarities, and there is much evidence that microenvironment, cytokines and signal pathways control tissue specificities and have a significant role in the process of carcinogenesis. Recent experimental results show that stem cells and tumor stem cells apparently play a key role in carcinogenesis. Tumors grow up, thanks to the activity of just few stem cells that continuously produce other proliferating progenitor tumor cells. Generally, tumor elements are thought to be either undifferentiated, or dedifferentiated cells. Actually, the truth is that tumors are made of more or less differentiated cells with variable rate of differentiation. We suppose that under certain conditions tumor stem cells may participate in regeneration without giving rise to tumor formation. It is also presumed that we may reprogram tumor stem cells and progenitor cells in a certain period of time and so initiate development of normal tissue. However, till now the real relation between normal and tumor cells is not clear. Finally, we wish to remind that plasticity of tumor and normal cells cannot be separated but should be considered as individual phenomenon expressing certain condition of an organism in time. This communication is only a probe and introduction into a discussion aimed at better understanding of carcinogenesis from the view of processes at the stem cell level. Stimulation of stem cell activation may lead to prophylactic approaches for therapy and prevention in carcinogenesis.