When Does A Patient Need A Stem Cell Transplant?

Let's first give a definition of a stem cell.
Stem cells have the remarkable potential to develop into many different cell types in the body during early life and growth. In addition, in many tissues they serve as a sort of internal repair system, dividing essentially without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential either to remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.
Stem cells are distinguished from other cell types by two important characteristics. First, they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity. Second, under certain physiologic or experimental conditions, they can be induced to become tissue- or organ-specific cells with special functions. In some organs, such as the gut and bone marrow, stem cells regularly divide to repair and replace worn out or damaged tissues. In other organs, however, such as the pancreas and the heart, stem cells only divide under special conditions.

 
A stem cell transplant is the infusion of healthy stem cells into your body. A stem cell transplant may be necessary if your bone marrow stops working and doesn't produce enough healthy stem cells. A stem cell transplant can help your body make enough healthy white blood cells, red blood cells or platelets, and reduce your risk of life-threatening infections, anemia and bleeding.
Although the procedure to replenish your body's supply of healthy blood-forming cells is generally called a stem cell transplant, it's also known as a bone marrow transplant or an umbilical cord blood transplant, depending on the source of the stem cells. Stem cell transplants can use cells from your own body (autologous stem cell transplant), or they can use stem cells from donors (allogenic stem cell transplant).

• Bone marrow transplantation and peripheral blood stem cell transplantation are procedures that restore stem cells that were destroyed by high doses of chemotherapy and/or radiation therapy.
• After being treated with high-dose anticancer drugs and/or radiation, the patient receives the harvested stem cells, which travel to the bone marrow and begin to produce new blood cells.
• A “mini-transplant” uses lower, less toxic doses of chemotherapy and/or radiation to prepare the patient for transplant.
• A “tandem transplant” involves two sequential courses of high-dose chemotherapy and stem cell transplant.
• The National Marrow Donor Program® maintains an international registry of volunteer stem cell donors.

Other Reasons For Bone Marrow Transplants

• Replace dysfunctional bone marrow. For instance, in aplastic anemia, a noncancerous condition, your bone marrow doesn't make enough new blood cells. A stem cell transplant procedure first destroys the dysfunctional marrow with powerful drugs or radiation, and then healthy stem cells are infused. If all goes well, the new stem cells migrate to the marrow and begin working normally.
• Destroy unhealthy bone marrow that may contain cancer cells. In the case of cancer, such as leukemia, a stem cell transplant procedure may first help rid the bone marrow of cancer cells. When healthy stem cells are then transplanted, normal cell production can resume. In addition, immune factors in the transplanted cells may help destroy any cancer cells that remain in your bone marrow.
•  For more information about stem cells :  www.mayoclinic.com 

http://stemcells.nih.gov  or  http://www.cancer.gov/cancertopics/factsheet/Therapy/bone-marrow-transplant