How are stem cells being used in cancer research?

Stem cells are being used in many ways. One idea, and it's still an idea, is that cancers actually arise from stem cells. These are the small number of cells in the body that are capable of reproducing indefinitely. Most cells in the body don't. They are usually either differentiated or can only go a few times and then they cop out. The idea is that cancer cells, because they can propagate indefinitely, arise from a stem cell compartment. This is still a new idea and there are a lot of good arguments going on about it, but we really don't know. The other idea is that if you expose a patient to a severe therapy and you start to kill off normal tissues, if you could keep the patient alive and repopulate those normal tissues, then the patient will make a full recovery. To do that you would need to propagate the stem cells in the patient in those tissues.