BONE MARROW TRANSPLANTATION OVERVIEW

Bone marrow transplantation (BMT), also called hematopoietic stem cell transplant or hematopoietic cell transplant, is a type of treatment for cancer (and a few other conditions as well). A review of the normal function of the bone marrow will help in the understanding of bone marrow transplantation.

Bone marrow functionBone marrow is the soft, spongy area in the center of some of the larger bones of the body. The marrow produces all of the different cells that make up the blood, such as red blood cells, white blood cells (of many different types), and platelets. All of these cells develop from a type of precursor cell found in the bone marrow, called a hematopoietic stem cell.

The body is able to direct hematopoietic stem cells to develop into the blood components needed at any given moment. This is a very active process, with the bone marrow producing millions of different cells every hour. Most of the stem cells stay in the marrow until they are transformed into the various blood components, which are then released into the blood stream. Small numbers of stem cells, however, can be found in the circulating blood, which allows them to be collected under certain circumstances. Various strategies can be employed to increase the number of hematopoietic stem cells in the blood prior to collection. (See 'Peripheral blood' below.)

Bone marrow transplantationSome of the most effective treatments for cancer, such as chemotherapy and radiation, are toxic to the bone marrow. In general, the higher the dose, the more toxic the effects on the bone marrow.

In bone marrow transplantation, you are given very high doses of chemotherapy or radiation therapy, which is intended to more effectively kill cancer cells and unfortunately also destroy all the normal cells developing in the bone marrow, including the critical stem cells. After the treatment, you must have a healthy supply of stem cells reintroduced, or transplanted. The transplanted cells then reestablish the blood cell production process in the bone marrow. Reduced doses of radiation or chemotherapy that do not completely destroy the bone marrow may be used in some settings. (See 'Non-myeloablative transplant' below.)

The cells that will be transplanted can be taken from the bone marrow (called a bone marrow transplant), from the bloodstream (called a peripheral blood stem cell transplant, which requires that you take medication to boost the number of hematopoietic stem cells in the blood), or occasionally from blood obtained from the umbilical cord at the time of birth of a normal newborn (called an umbilical cord blood transplant).

TYPES OF BONE MARROW TRANSPLANTATION

There are two main types of bone marrow transplantation: autologous and allogeneic.

Autologous transplantIn autologous transplantation, your own hematopoietic stem cells are removed before the high dose chemotherapy or radiation is given, and they are then frozen for storage and later use. After your chemotherapy or radiation is complete, the harvested cells are thawed and returned to you.

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Bone marrow transplantation (stem cell transplantation)