Although you may think of your body as a fairly permanent structure, most of it is in a state of constant flux, as old cells are discarded and new ones generated in their place. Each type of tissue has its own turnover time, depending in part on the workload endured by its cells.

Adult stem cells are undifferentiated cells, found throughout the body after embryonic development, which multiply by cell division to replenish dying cells and regenerate damaged tissue. Adult stem cells support tissue and organ turnover throughout life by maintaining a delicate balance between apoptosis and tissue-specific cellular proliferation and differentiation.

Regenerative medicine is the use of tissue engineering and molecular biology to improve or replace biological function in human cells, tissues and organs. Research on adult stem cells has generated a great deal of excitement in this regard. 

Cancer survival rates decrease with age, in part because the efficacy of cancer therapies declines in older individuals.

Stem cell transplants have been widely used as a treatment for cancer since the 1960s. In 2010, the FDA approved Provenge, a product designed to treat late-stage prostate cancer.