Stem cells are unspecialized cells that have the capability to become many different types of cells. Stem cells in the bone marrow are the source of all the different normal blood cells. High doses of chemotherapy drugs or radiation therapy can kill cancer cells but often also kills the person's stem cells, which prevents the bone marrow from producing normal blood cells.
Stem cell transplantation replaces the killed stem cells with healthy stem cells from a donor. Donors can be the person with cancer (an autotransplant) or another genetically matched related or unrelated person (an allotransplant). The stem cells may be taken from a donor's bone marrow, but it is easier and almost as effective to get the stem cells from the donor's blood. Stem cell transplants allow doctors to give high doses of chemotherapy to treat leukemias and some lymphomas.
