The doses of chemotherapy drugs that doctors can give are limited by the serious side effects they can cause. Even though higher doses of these drugs might kill more cancer cells, they can’t be given because they could severely damage the bone marrow, which is where new blood cells are formed. This could lead to life-threatening infections, bleeding, and other problems due to low blood cell counts.
Doctors can sometimes use a stem cell transplant (SCT) to give higher doses of chemotherapy (sometimes combined with radiation therapy) than could normally be given. After the treatment is finished, the patient gets an infusion of blood-forming stem cells to restore their bone marrow.
The blood-forming stem cells used for a transplant can come either from the blood or from the bone marrow. Sometimes stem cells from a baby’s umbilical cord blood are used.
Types of transplants
The 2 main types of stem cell transplants differ based on whom the blood-forming stem cells come from.
Allogeneic stem cell transplant
This is the most common type of SCT used to treat acute myeloid leukemia (AML). In an allogeneic SCT, the stem cells come from someone other than the patient – usually a donor whose tissue type (also known as the HLA type) closely matches the patient’s. 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.
The best donor is often a close relative, such as a brother or sister, if they are a good match. If no close relatives match, stem cells might be available from a matched unrelated donor (MUD), an unrelated volunteer whose tissue type matches that of the patient. But the use of stem cells from a MUD is linked to more complications. 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.
In AML, using an allogeneic SCT is preferred over an autologous SCT (see below) because leukemia is a disease of the blood and bone marrow, so giving the patient his or her own cells back may mean giving them back some leukemia cells as well. Donor cells are also helpful because of the “graft-versus-leukemia” effect. When the donor immune cells are infused into the body, 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.
Allogeneic transplants can have serious risks and side effects, so patients typically need to be younger and relatively healthy to be good candidates. Another challenge is that it can sometimes be difficult to find a matched donor.
One of the most serious complications of allogeneic SCTs is known as graft-versus-host disease (GVHD). It happens when the patient’s immune system is taken over by that of the donor. When this happens, the donor immune system may consider the patient’s own body tissues to be foreign and attacks them.
Symptoms can include severe skin rashes, itching, mouth sores (which can affect eating), nausea, and severe diarrhea. Liver damage can cause yellowing of the skin and eyes (jaundice). The lungs can also be damaged. The patient may also become easily fatigued and develop muscle aches. Sometimes GVHD can become disabling, and if it is severe enough, it can be life-threatening. Drugs that affect the immune system may be given to try to control it.
Non-myeloablative transplant (mini-transplant): Many older people can’t tolerate a standard allogeneic transplant that uses high doses of chemo. Some may still be able to get a non-myeloablative transplant (also known as a mini-transplant or reduced-intensity transplant), where they get lower doses of chemo and radiation that don’t completely destroy the cells in their bone marrow. They then get the allogeneic (donor) stem cells. These cells enter the body and establish a new immune system, which sees the leukemia cells as foreign and attacks them (a “graft-versus-leukemia” effect).
A non-myeloablative transplant can still sometimes work with much less toxicity. In fact, a patient can receive the transplant as an outpatient. The major complication is graft-versus-host disease (described below).
Many doctors still consider this an experimental procedure for AML, and studies are under way to determine how useful it may be.
Autologous stem cell transplant
In an autologous transplant, a patient’s own stem cells are removed from his or her bone marrow or blood. They are frozen and stored while the person 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 put back (reinfused) into the patient’s blood after treatment.
Autologous transplants are sometimes used for people with AML who are in remission after initial treatment and who don’t have a matched donor for an allogeneic transplant. Some doctors feel that it is better than standard “consolidation” chemotherapy (see “Typical treatment of acute myeloid leukemia”) for these people, but not all doctors agree with this.
Autologous transplants are generally easier to tolerate than allogeneic transplants, because the patient is getting his or her own cells back, which lowers the risk of some complications. But the high-dose chemo can still cause major side effects. This type of transplant can be done in any otherwise healthy person, although very old patients might not be suitable.
One problem with autologous transplants is that it’s hard to separate normal stem cells from leukemia cells in the bone marrow or blood samples. Even after purging (treating the stem cells in the lab to try to kill or remove any remaining leukemia cells), there is the risk of returning some leukemia cells with the stem cell transplant.
The transplant procedure
Blood-forming stem cells from the bone marrow or blood are collected, frozen, and stored. The patient gets high-dose chemo and sometimes also 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 cancer cells in the body. They also kill the normal cells of the bone marrow and the immune system. After these treatments, the frozen stem cells are thawed and given 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.
In an allogeneic SCT, the person getting the transplant is given drugs to keep the new immune system in check. For the next few weeks the patient will get regular blood tests and supportive therapies as needed, which might include antibiotics, red blood cell or platelet transfusions, other medicines, and help with nutrition.
Usually within a couple of weeks after the stem cells have been infused, they begin making new white blood cells. This is followed by new platelets and, several weeks later, new red blood cells.
Patients need to stay in the hospital until their neutrophil count (often called the ANC) rises to a safer level (at least 500, but sometimes 1,500 is the target). Other factors also affect how long a person needs to stay in the hospital, like the type of transplant, the presence of an infection or other complications, and the ability of the patient to be followed-up in the outpatient clinic. After discharge from the hospital, the patient is seen in the outpatient clinic for several weeks, often daily. Because platelet counts take longer to return to a safe level, patients may get platelet transfusions as an outpatient.
A stem cell transplant is a complex treatment that can sometimes cause life-threatening side effects. If the doctors think you might benefit from a transplant, it should be done at a hospital where the staff has experience with the procedure and with managing the recovery phase. Some stem cell transplant programs might not have experience in certain types of transplants, especially transplants from unrelated donors.
SCT is very expensive (costing well over $100,000) and often requires a lengthy hospital stay. Because some types of SCT may be viewed as experimental by insurance companies, they may not pay for the procedure. It is important to find out what your insurer will cover before deciding on a transplant to get an idea of what you might have to pay.
Possible side effects
Side effects from SCT are generally divided into early and long-term effects.
Early or short-term effects: The early complications and side effects are basically the same as those caused by any other type of chemotherapy (see “Chemotherapy for acute myeloid leukemia”), although they tend to be more severe. 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 infection. 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.
A possible serious side effect of allogeneic transplants is graft-versus-host disease, which is described above.
Long-term side effects: Some complications and side effects can remain for a long time or might not occur until months or years after the transplant. These include:
- Chronic graft-versus-host disease (only in allogeneic transplants)
- Loss of fertility
- Damage to the lungs, causing shortness of breath
- Damage to the thyroid gland, causing problems with metabolism
- Cataracts (damage to the lens of the eye that can affect vision)
- Bone damage called aseptic necrosis (where the bone dies because of poor blood supply). If damage is severe, the patient might need to have part of the bone and the joint replaced.
- Development of another cancer years later
For more on stem cell transplants, see Stem Cell Transplant (Peripheral Blood, Bone Marrow, and Cord Blood Transplants).
Last Revised: 02/22/2016