Preface

Somatic stem cells (SSCs) or adult stem cells can be found in almost all tissues of the body. They can self-renew and proliferate and differentiate to produce some or all of the cells in a tissue or an organ. SSCs play a very important role in the maintenance of normal tissue homeostasis by replenishing dying cells and regenerating damaged tissues for the entire lifespan of an organism. Normally, SSCs reside in a special microenvironment called the “stem cell niche” which can significantly influence their fate. In addition, maintenance of genomic stability has been shown to be crucial for the preservation of SSC longevity and prevention of SSCs from transformation. Therefore, perturbation of the ability of SSCs to self-renew, proliferate and differentiate to produce progeny and disturbance of the stem cell niche microenvironment have been implicated in various pathological conditions and a variety of disease processes, including normal tissue injury induced by cancer treatment with chemotherapy and ionizing radiation (IR). Furthermore, because SSCs can self-renew, they are long lived cells that represent ideal cellular targets for acquisition of multiple mutations which may transform SSCs to cancer stem cells (CSCs) to cause malignancies. Like SSCs, CSCs can also self-renew and have high tumorigenic potential. In addition, CSCs are usually more resistant to chemotherapy and IR than SSCs. Failure to eradicate CSCs may be responsible for tumor recurrence after cancer treatment.