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Salem Health: Cancer Stem Cell Transplants Category: Procedures Definition Stem cells are early blood-forming cells, also referred to as hematopoietic cells, that grow and mature in the bone marrow but can circulate in blood as well. Hematopoietic cells are immature cells capable of dividing and developing into all blood cell types, including cells of the immune system. Stem cell transplantation involves replenishing hematopoietic cells following high dose chemotherapy and radiation by infusing stem cells into the patient's body. Stem cell transplants are classified based on the source of stem cells, including where they are collected and from which individual they are donated. Stem cells may be collected from the bone marrow, peripheral blood, or umbilical cord. To represent the source of stem cells, the terms "bone marrow transplantation," "peripheral blood stem cell transplantation," and "umbilical cord transplantation" are used. There are important advantages and disadvantages associated with using stem cells from these different sources. Stem cell transplants are also classified by who donates them. If stem cells come from the patient, they are termed "autologous." They may also come from an identical twin, in which case they are called "syngeneic," or from someone other than the patient, when they are called "allogeneic." Allogeneic stem cells are further classified by whether the individual donating the stem cells is related or unrelated to the patient. The best-known stem cell therapy is bone marrow transplantation (BMT). While most blood stem cells reside in bone marrow, a small number are present in the blood. These multipotent peripheral blood stem cells (PBSC), like bone marrow stem cells, can be used to treat leukemia and other cancers. PBSC transplants are less invasive than BMT because PBSC can be collected from blood, although the difficulty arises in collecting sufficient numbers to perform a transplant. Stem cells from umbilical cords can also be used in stem cell transplants. Newborns no longer need umbilical cords, a tissue which has traditionally been discarded during birth. In the 1990's it was realized that umbilical cord blood is rich in multipotent stem cells and thus useful against health problems similar to those treated with bone marrow and peripheral blood stem cells. An important advantage of umbilical cord stem cell transplants is reduced rejection, probably because the cells have not yet developed features that can be recognized by the recipient's immune system. Similarly, because umbilical cord blood lacks well-developed immune cells, there is less chance that transplanted cells will attack the recipient's body, a problem called graft-versus-host disease. Bone marrow or PBSC transplants can be either autologous or allogeneic. An autologous transplant requires infusion of the patient's own hematopoietic cells to restore the body's ability to make blood cells. In an autologous stem cell transplant, stem cells are collected from the patient's bone marrow or blood before high-dose chemotherapy is administered. An allogeneic stem cell transplant combines high-dose therapy with immunotherapy. High-dose therapy is administered to treat the cancer as in autologous transplants, but is followed by an infusion of stem cells from a donor's blood or bone marrow. The donor cells supply the patient with new blood cells as well as a new immune system that helps eliminate any residual disease, a process called immunotherapy. Allogeneic transplants can vary, based on intensity. A stem cell transplant that uses high-dose chemotherapy combined with radiation to stop bone marrow function (to allow donor cells to "engraft," or grow) is referred to as "myeloablative." A nonmyeloablative transplant, sometimes called a "mini-transplant," uses lower radiation and chemotherapy doses to allow the bone marrow to function until donor cells replace the patient's marrow. Cancers Treated Stem cell transplants are most commonly used to treat hematological (blood) malignancies such as chronic leukemias, lymphomas, and myelomas. They are also used to treat cancers such as neuroblastoma and selected solid tumors. Why Performed High-dose chemotherapy is the best treatment for certain types of cancers. One of the major side effects of high-dose chemotherapy is destruction of bone marrow stem cells. Stem cell transplants can help restore or replace these cells. Using stem cell transplants in cancer treatment makes it possible for patients to receive very high doses of chemotherapy or radiation therapy. In addition, immune factors in the transplanted cells may help destroy any cancer cells remaining in the bone marrow. Patient Preparation Usually, patients remain at home until the time the transplant is scheduled. During this time, the patient is often encouraged to build strength and maintain a healthy diet. An important part of patient preparation is researching insurance coverage in order to maximize care. If not nearby, the patient should make arrangements to stay closer to the hospital. It is also necessary to make arrangements for caregiving for up to four months. Caregiving will be needed for help with household chores, grocery shopping, food preparation, medications, central venous catheter care, monitoring food and fluid intake, cleaning, companionship, and transportation. Steps of the Procedure Once donor stem cells become available, many tests and procedures are conducted to ensure the patient is healthy enough to receive the transplant. A catheter, called a central line, is inserted intravenously in the chest area near the neck. The central line remains in place for duration of the treatment and will be used for infusion of stem cells. The central line is also used to collect blood samples, administer chemotherapy, and provide blood transfusions and nutrition. The next step in the procedure is called "conditioning" and occurs the week before the transplant. During conditioning, the patient undergoes chemotherapy and possibly radiation in order to destroy cancer cells and suppress the immune system to prevent the patient's body from rejecting transplanted stem cells. Conditioning may be conducted in the hospital or on an outpatient basis. Even if conducted as outpatient, hospitalization for side effects may be required. Numerous side effects may occur and include nausea and vomiting, diarrhea, hair loss, mouth sores or ulcers, infections, bleeding, infertility, sterility, premature menopause, anemia, fatigue, cataracts, organ failure, and secondary cancers. Medications may help reduce side effects. After the patient has been treated with high-dose anticancer drugs or radiation during the conditioning process, stem cells are introduced into the patient's bloodstream intravenously. After the Procedure If the transplant is successful, stem cells will migrate into the patient's bone marrow and begin producing healthy white blood cells, red blood cells, and platelets. This process occurs within about 2 to 4 weeks and is known as "engraftment." Until the new stem cells begin functioning, transplant recipients will be at risk for complications such as infections and bleeding. Complete recovery of immune function can take several months for autologous transplant recipients and up to two years for patients receiving allogeneic or syngeneic transplants. Doctors conduct various tests to confirm that cancer cells have been eliminated and new blood cells are being produced. Bone marrow aspiration, the removal of a small sample of bone marrow, may be conducted to determine if the transplant is working. Some patients can leave the hospital within three to five weeks, but others may require longer hospitalization. Risks Stem cell transplants are associated with many risks and complications, some potentially fatal. Complications that can arise include stem cell failure, organ and blood vessel damage, cataracts, secondary cancers, and death. Other major risks associated with stem cell transplants are increased susceptibility to infection and bleeding. Stem cell transplant recipients may experience short-term side effects such as nausea, vomiting, fatigue, loss of appetite, mouth sores, hair loss, and skin reactions. A very serious complication known as graft-versus-host disease (GVHD) may occur when immune cells from the donor attack the patient's cells. Generally, the most commonly damaged organs in a GVHD response are the skin, liver, and intestines. GVHD is treated with steroids or other immunosuppressive agents. Results Stem cell transplants can extend the life of transplant recipients and cause some cancers to go into remission. Many transplant recipients enjoy a good quality of life and are able to resume their normal activities. Side effects and transplant success vary among recipients, with some patients experiencing very few complications while others experience numerous problems. C. J. Walsh, Ph.D. For Further Information Cant, A. J. Practical Hematopoietic Stem Cell Transplantation. Malden, Mass.: Blackwell, 2007. Stewart, S. Bone Marrow Transplants: A Book of Basics. Highland Park, Ill.: Blood and Marrow Transplant Information Network, 1995. Stewart, S. Bone Marrow and Blood Stem Cell Transplants: A Guide for Patients. Highland Park, Ill.: Blood and Marrow Transplant Information Network, 2002. Other Resources Blood and Marrow Transplant Information Network http://www.bmtinfonet.org National Cancer Institute www.cancer.gov Cancerbakcup http://www.cancerbackup.org.uk Mayo Clinic http://www.mayoclinic.com See Also Bone marrow transplantation; graft-versus-host disease; umbilical cord blood transplant. |
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