Bone Marrow Transplantation

Definition

Bone Marrow Transplantation is replacing or transplanting healthy bone marrow to replace defective bone marrow.

Description

Bone marrow is a soft, spongy material found inside bones. Bone marrow contains immature (or stem) cells that are capable of continuously producing new blood cells. This is what helps make bone marrow the "factory" for normal blood cells - the red cells that carry oxygen, the white cells that fight infections, and the platelets that help clot blood.

Bone marrow can sometimes be defective - for example, not producing enough normal blood cells. Doctors long ago realized that if defective bone marrow could be replaced or transplanted with normal marrow from another individual, many lives could be prolonged. But only in the past 25 years has medical knowledge advanced to the point where effective bone marrow transplantation techniques could be developed.

These techniques involve the intravenous administration of immature blood cells capable of reproducing themselves and repopulating an empty or defective bone marrow. Replacing the defective bone marrow of an otherwise healthy person is one use of transplantation techniques. But at least 90 percent of all bone marrow transplants are performed to treat cancer.

The main purpose of BMT in cancer treatment is to make it possible for patients to receive very high doses of chemotherapy and/or radiation - doses so high that they severely damage and may destroy the patient's marrow. BMT makes it possible for patients to receive these higher and potentially more effective doses of radiation therapy or chemotherapy because marrow damaged by treatment is replaced with healthy marrow.

Without healthy blood cells from the new marrow, the patient would be susceptible to infections and unable to fight them. In patients with leukemia, BMT also provides marrow that is free of disease either from a donor or from the patient after the marrow is treated to remove cancer cells.

BMT is now considered to be a standard treatment option for some patients with several types of cancer - among them neuroblastoma (a childhood cancer) and certain leukemias and lymphomas.

Types

There are several types of bone marrow transplantation.

The most common type is autologous transplantation (ABMT). In this procedure the patient's own marrow is used and is extracted from their bones before the treatment begins. This marrow is then treated to separate the healthy cells from any cancer cells that may be present, and it is finally stored until it can be reinfused or transplanted to replace the damaged marrow.

Another type of bone marrow transplantation is called peripheral blood stem cell transplantation (PBSCT). Blood is withdrawn from the patient's vein via a catheter and is filtered to separate stem cells from the rest of the blood. These peripheral (circulating) blood stem cells are then frozen so that they can be transplanted after treatment.

For allogeneic transplantation, the source of the marrow is another person - usually the patient's sibling or parent, but unrelated donors are sometimes used. In this procedure the donor's immune system cells are transplanted along with the marrow, providing the recipient with both immune and bone marrow function.

In the last few years the results of placental stem cell or umbilical cord blood transplantations have shown promise as another method of transplantation. Umbilical cord blood is removed from the umbilical cord after a baby is born. The blood is tested for infectious and genetic diseases and then frozen. At transplantation time, it is thawed and transfused into the arm vein.

Procedure

In newborn children, essentially all bones have active marrow. In adults, active marrow is found in the center of the pelvic bones, ribs, spine and collarbones. When an appropriate donor is identified, active marrow is usually removed from these bones with needles and a syringe. In some circumstances, it is possible to remove stem cells from the blood.

Most bone marrow transplants involve extracting bone marrow from the bones of the pelvis by repeated needle punctures. The donor receives an anesthetic during this process because it takes numerous needle punctures to remove enough marrow for a transplant - about 500 to 1,000 cc (one or two pints).

Shortly after chemotherapy (with or without radiation therapy) is completed, the patient receives the donated marrow through an intravenous catheter. This infusion of marrow is called the rescue process. The marrow travels through the bloodstream to the bone marrow, where it begins to manufacture new white blood cells, red blood cells and platelets.

Risks

The transplant procedure is fraught with risk. The specific risks associated with BMT include:

1. Secondary cancers. High dose chemotherapy and radiation lead to secondary malignancies in about 2 to 10 percent of autologous transplants patients and 2 to 3 percent in allogenic transplants.

2. Infections.

3. Graft versus host disease. This disease occurs when cells in the donated marrow (the graft) identify the recipient's body (the host) as foreign and attack it. Weight loss, bacterial infections, skin and organ problems can occur up years after transplantation and may be fatal.

4. Infertility/sterility.

5. Various psychological responses to serious disease and complex treatment.

Questions to Ask Your Doctor

Is a bone marrow transplant needed?

What benefits can be expected from a transplant?

How and where does bone marrow come from?

Is there a donor association that is called when bone marrow is needed?

How will the procedure be performed?

How many have you performed?

Will a catheter be inserted? When will this be done?

What are the risks and side effects?

How long is the hospital stay?

What changes in normal activities will be required?

What supportive care will be available?