A stem cell transplant (SCT) can sometimes be used for children whose chances of being cured are poor with standard or even intensive chemotherapy. SCT allows doctors to use even higher doses of chemotherapy than would normally be tolerated.
High-dose chemotherapy destroys the bone marrow, which is where new blood cells are formed. This could lead to life-threatening infections, bleeding, and other problems caused by low blood cell counts. A stem cell transplant (SCT) allows doctors to use higher doses of chemotherapy and, sometimes, radiation therapy. After treatment is finished, the child receives a transplant of blood-forming stem cells to restore the bone marrow.
Blood-forming stem cells used for a transplant are obtained either from the blood (for a peripheral blood stem cell transplant [PBSCT] or an umbilical cord blood transplant) or from the bone marrow (for a bone marrow transplant, or BMT). Bone marrow transplants were more common in the past, but they have largely been replaced by PBSCT and cord blood transplants.
Types of transplants
There are 2 main types of stem cell transplants: allogeneic and autologous. They differ in the source of the blood-forming stem cells.
Allogeneic stem cell transplant: For childhood leukemia, the blood-forming stem cells are generally donated from another person. This is called an allogeneic transplant, meaning the cells come from someone else. The donor's tissue type (also known as the HLA type) should be almost identical to the patient's tissue type to help prevent the risk of major problems with the transplant. Tissue type is based on certain substances on the surface of cells in the body. These substances can cause the immune system to react against the cells. Therefore, the closer a tissue "match" is between the donor and the recipient, the better the chance the transplanted cells will "take" and begin making new blood cells.
Usually the donor is a brother or sister if they have the same tissue type as the patient. Rarely, it may be an HLA-matched, unrelated donor – a stranger who has volunteered to donate blood-forming stem cells. Sometimes umbilical cord stem cells are used. These stem cells come from blood drained from the umbilical cord and placenta after a baby is born and the umbilical cord is cut. (This blood is rich in stem cells.) The blood is then frozen and stored until it is needed by someone with the same tissue type.
Allogeneic stem cell transplants are the most common type of transplant for childhood leukemias.
Autologous stem cell transplant: In an autologous transplant, the patient's own stem cells are removed from his or her bone marrow (bone marrow stem cells) or bloodstream (peripheral blood stem cells, PBSCs). They are frozen and stored while the child gets treatment (high-dose chemotherapy and/or radiation). A process called purging may be used to try to remove any leukemia cells in the samples. The stem cells are then reinfused into the child's blood after treatment.
This type of transplant is rarely used for childhood leukemia, because the risk that the leukemia will come back (relapse) after treatment is greater than with an allogeneic transplant. There are a couple of reasons for this. One concern is that there are leukemia cells in the child's blood and bone marrow, so there may be a risk of returning these leukemia cells to the child after treatment. Purging can reduce this risk, but it may not eliminate it completely. An allogeneic transplant may also be more effective than an autologous transplant because of the "graft versus leukemia" effect. When the donor immune cells are infused into the body as part of the transplant, they may recognize any remaining leukemia cells as being foreign to them and attack them. This effect doesn't happen with autologous stem cell transplants.
When SCT may be used
SCT may be used for a child with ALL whose leukemia relapses early after going into remission. It is less clear if SCT should be used for those children with ALL who relapse more than 6 months after finishing their initial chemotherapy. These children will often do well with another round of standard dose chemotherapy. SCT may also be recommended for children with some rarer forms of ALL, such as those whose leukemias have the "Philadelphia chromosome" (translocation between chromosomes 9 and 22) or those with T-cell ALL that doesn't respond well to initial treatment.
Because AML relapses more often than ALL, many doctors recommend SCT for children with AML right after they have gone into remission, if the child has a brother or sister with the same tissue type who can donate stem cells for the transplant. This is especially true if there is a very high risk of relapse (as seen with some subtypes of AML or certain chromosome changes). But there is still some debate about which children with AML need this type of intensive treatment. If a child with AML relapses after his or her first round of standard chemotherapy, most doctors will recommend SCT as soon as the child goes into remission again.
In either case, it is important that the patient is in remission before getting a stem cell transplant. Otherwise, the leukemia is more likely to return.
What SCT involves
Stem cells collected from a donor or the patient are carefully frozen and stored. The child then receives high-dose chemotherapy and sometimes radiation treatment to the entire body. (Radiation shields are used to protect the lungs, heart, and kidneys from damage during radiation therapy.)
These treatments are meant to destroy any remaining cancer cells. But they also kill the normal cells in the bone marrow. After treatment, the frozen stem cells are thawed and returned to the body as a blood transfusion. The stem cells settle into the patient's bone marrow over the next several days and start to grow and make new blood cells.
For the next 3 to 4 weeks the patient is at high risk for serious infections because of a low white blood cell count, as well as bleeding because of a low platelet count. During this time, blood and platelet transfusions and treatment with IV antibiotics are often used to prevent or treat infections or bleeding problems.
Patients usually stay in the hospital in protective isolation (guarding against exposure to germs) until part of their white blood cell count (known as the absolute neutrophil count, or ANC) rises above 500. They may be able to leave the hospital when their ANC is near 1,000. The child is then seen in an outpatient clinic almost every day for several weeks. Because platelet counts take longer to return to a safe level, they may get platelet transfusions as an outpatient.
Practical points
The stem cell transplant procedure is a complex treatment. If the doctors think your child may benefit from a transplant, the best place to have this done is at a nationally recognized cancer center where the staff has experience with the procedure and with managing the recovery period.
A stem cell transplant often requires a lengthy hospital stay and can be very expensive (costing more than $100,000). Because the procedure is so expensive, you should be sure to get a written approval from your insurer before treatment if it is recommended for your child.
Possible side effects
The possible side effects from SCT are generally divided into early and long-term effects.
Short-term side effects
The early complications and side effects are basically the same as those caused by any other type of high-dose chemotherapy (see the "Chemotherapy" section of this document), and are caused by damage to the bone marrow and other quickly dividing tissues of the body. They can include low blood cell counts (with fatigue and an increased risk of infection and bleeding), nausea, vomiting, loss of appetite, mouth sores, and hair loss.
One of the most common and serious short-term effects is the increased risk of serious infections from bacteria, viruses, or fungi. Antibiotics are often given to try to prevent this from happening. Other side effects, like low red blood cell and platelet counts, may require blood product transfusions or other treatments.
Long-term side effects
Some complications and side effects can persist for a long time or may not occur until months or years after the transplant. These can include:
- Graft-versus-host disease (GVHD), which can occur in allogeneic (donor) transplants. This happens when the donor immune system cells attack tissues of the patient's skin, liver, and digestive tract. Symptoms can include weakness, fatigue, dry mouth, rashes, nausea, diarrhea, yellowing of the skin and eyes (jaundice), and muscle aches. In severe cases, GVHD can be life-threatening. GVHD is often described as either acute or chronic, based on how soon after the transplant it begins. Drugs that weaken the immune system are often given to try to keep GVHD under control.
- Radiation damage to the lungs
- Problems with the thyroid or other hormone-making glands
- Problems with fertility
- Problems with bone growth
Be sure to talk to your child's doctor before the transplant to learn about possible long-term effects your child may have. More information on possible long-term effects can be found in the section, "What happens after treatment for childhood leukemia?"
To learn more about stem cell transplants, see our document, Bone Marrow and Peripheral Blood Stem Cell Transplant.
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