Cancer Stem Cells of Head and Neck Squamous Cell Carcinoma

Homeostasis of most tissues and organs is maintained by tissue-specific somatic or adult stem cells (SCs) and their early progenitors possessing two main properties: self-renewal and differentiation. To fulfil these two functions, they must undergo either symmetrical division for stem cell expansion, necessary after injury for example, or asymmetrical division for stem cell maintenance and progenitor production. The “cancer stem cell hypothesis” postulates that tumours arise from adult stem cells called cancer stem cells (CSCs) that possess stem cell properties. There is growing evidence that most solid tumours and haematological malignancies are driven by CSCs as a result of advances in stem cell biology and the development of animal models. This has fundamental implications for understanding the biology of cancers and also for developing new therapeutic strategies. The recent characterisation of CSC in head and neck squamous cell carcinoma (HNSCC) prompted us to re-examine the disease development and to discuss the limited effects of conventional therapies.