[Cancer stem cells as a possible source of tumor initiation and progression]

Cancer stem cells may be a source of malignant tumors as well as their relapses after treatment and metastases. They share many features with normal tissue stem cells but also possess mutations and other genetic and epigenetic changes that make them tumorigenic and resistant to conventional cancer therapies. The source of cancer stem cells is discussed: they may originate from normal tissue stem cells as a result of their mutations or deregulation of signaling pathways or alternatively from differentiated tumor cells as a result of dedifferentiation during tumor development. Cancer stem cells reside in a special tumor microenvironment (niche) that regulates their functions. A number of signaling pathways and molecules participate in regulating cancer stem cells features. And although there are some inconsistencies concerning cancer stem cells, their existence may change our view on cancer progression and help to develop new strategies of cancer treatment.