致癌与突变杂志

抽象的

The Common Genesis of All Cancers

Pushpam Kumar Sinha

It is a commonly held belief nowadays that cancer originates in tissue-specific adult stem cells. Most of the tissues in human body have adult stem cells at their base. The difference between embryonic stem cell and adult stem cell is that whereas the former, through a carefully orchestrated cellular program of development genes, can give rise to terminally differentiated cells of all types, the later can repair the terminally differentiated tissue by giving rise to cells of few types specific to the tissue. In a majority of tissues the adult stem cells are relatively quiet, swinging into action only on signals of damage or injury to tissue. One of the exceptions of this is the adult stem cell of intestinal epithelium, which is continuously in action as the differentiated cells of intestinal epithelium are continuously shed into the lumen. The adult stem cells have the property of self-renewal: they can undergo asymmetric cell division to give rise to two distinct daughter cells one of which is the exact copy of mother stem cell and the other is a partially differentiated progenitor cell or progeny, and symmetric cell division to give rise to two identical daughter cells which are exact replicas of mother stem cells. The progenitors further undergo cell division to yield terminally differentiated cells having specific morphologies and functions. The rates of self-renewal, apoptosis and differentiation of adult stem cells and their progenitor cells is very tightly regulated to achieve homeostasis, i.e. steady state where in the number of adult stem cells, progenitor cells and terminally differentiated cells attain a constant value. It has been suggested that cancer results by multiple mutations in adult stem cells and or progenitor cells which disturbs the balance between rates of self-renewal, apoptosis and differentiation leading to unsteady state. Though adult stem cells of different tissues are different from each other, the similarity in their fates and properties both under normal conditions and carcinogenic conditions strongly suggest that there must be a common genesis of all cancers, at least of those organs that have adult stem cell in their lineage. Through this review I investigate the possibility of common genesis of all cancers.