Stem cells as a two edged sword--from regeneration to tumor formation.

Evidence has accumulated that quiescent stem cells or cells developmentally closely related to them distributed in various organs may be a cellular origin of cancer development. In support of this notion, stem cells (SC) are long-lived cells with distinctive properties of self-renewal and has the potential to proliferate extensively. Given these features, it's possible that they may become the subject of consecutive accumulated mutations that are crucial for initiation of cancer. Therefore, mutations that occur in normal stem cells might lead to their malignant transformation and tumor initiation. Furthermore, many biological features of normal and cancer SC such as the physiological trafficking of normal and metastasis of cancer stem cells involve similar molecular mechanisms, and we discuss these similarities here.