Stem Cells and Cancer: the Cancer Stem Cell (CSC) Model

Abstract

Cancer stem cells (CSCs) can be defined as cells within the tumour which are tumour-initiating and which possess the capacity to self renew and generate the heterogenous lineages of cancer cells that comprise the tumour. They are functionally characterized by their abilities to self-renew, differentiate and form tumours in immunocompromised mice. Only a certain subpopulation of cells within the tumour possesses these abilities. CSCs have been isolated from a variety of cancers and are believed to play pivotal roles in tumour initiation, tumour progression and metastasis as well as in tumour recurrence. CSCs may arise from normal stem cells in tissue, which undergo a loss of regulation of proliferation; alternatively, they can arise from normal somatic cells which acquire stem cell like characteristics. At the molecular level, intracellular signalling pathways involved in normal stem cell self-renewal and proliferation often show dysregulation or aberrant activation in CSCs. Inherent mechanisms present in CSCs appear to render them comparatively more resistant to conventional anti-cancer approaches like chemotherapy and radiotherapy. Thus, for maximal effectiveness, anti-cancer therapies would probably need to target critical molecular pathways essential for CSC self-renewal, proliferation and survival. This review provides an overview of CSCs, their roles in various cancers and discusses their probable origins, molecular pathways involved in their functions and some possible molecular methods for targeting CSCs which may hold promise for developing therapies for alleviation of cancer.