The stem cell concept in oral mucosa and in cancer

Oral mucosa is a highly dynamic tissue that rapidly replaces its structure and contributes to oral health by maintaining an intact barrier that protects the underlying tissues in the face of much environmental stress. The rapid rate of mucosal renewal has been known for many years but it is only now becoming apparent that mucosal renewal and repair depends ultimately on a small subpopulation of cells, known as stem cells. Only stem cells have the ability to continuously generate new cells for the whole lifetime and when they divide they both renew themselves and produce hierarchies of other cells that differentiate for tissue function. This has many implications for tissue renewal and, of paticular interest, important roles of stem cells in the development and treatment of cancer are emerging. Cancers appear to arise as a result of changes in stem cells and altered stem cells are then responsible for driving tumour growth and metastasis. Within a cancer, as in normal tissue, stem cells are few and difficult to identify. This complicates the need to identify their special characteristics and ensure that they are included within the targets of therapeutic procedures. An additional interesting feature of normal stem cells is that they appear to have marked plasticity and, at least under experimental or pathological conditions, they can change to generate many different types of tissues. This is contrary to previous ideas about the stability of cell phenotypes after development, stem cells and offers a range of promising new tissue engineering techniques for the restoration of diseased or damaged tissues.