Cancer stem cells - new and potentially important targets for the therapy of oral squamous cell carcinoma

There is increasing evidence that the growth and spread of cancers is driven by a small subpopulation of cancer stem cells (CSCs) - the only cells that are capable of long-term self-renewal and generation of the phenotypically diverse tumour cell population. Current failure of cancer therapies may be due to their lesser effect on potentially quiescent CSCs which remain vital and retain their full capacity to repopulate the tumour. Treatment strategies for the elimination of cancer therefore need to consider the consequences of the presence of CSCs. However, the development of new CSC-targeted strategies is currently hindered by the lack of reliable markers for the identification of CSCs and the poor understanding of their behaviour and fate determinants. Recent studies of cell lines derived from oral squamous cell carcinoma (OSCC) indicate the presence of subpopulations of cells with phenotypic and behavioural characteristics corresponding to both normal epithelial stem cells and to cells capable of initiating tumours in vivo. The present review discusses the relevance to OSCC of current CSC concepts, the state of various methods for CSC identification, characterization and isolation (clonal functional assay, cell sorting based on surface markers or uptake of Hoechst dye), and possible new approaches to therapy.