Bone marrow transplants help patients replace damaged bone marrow with healthy donor marrow. The bone marrow contains stem cells that grow into red blood cells, white blood cells and platelets.

The vast majority of bone marrow transplants are performed to treat cancer patients whose marrow has been damaged by chemotherapy or radiation treatments. Transplants are also performed to replace defective bone marrow in patients without cancer.  

Bone marrow is the soft and spongy material found inside a person’s bones. Hematopoietic (blood-forming) stem cells are found in the marrow. These cells divide and form any one of the following:

• Additional hematopoietic stem cells. These cells can then produce additional cells of any type.
  
  
• White blood cells. Protect the body from diseases, including potentially life-threatening infections.
  
  
• Red blood cells. Carry oxygen to all parts of the body and take carbon dioxide from the cells back to the lungs to be expelled from the body.
  
  
• Platelets. Help clot blood to prevent excessive bleeding or bruising.

While most of the body’s hematopoietic cells are found in bone marrow, some appear in the bloodstream. These are called peripheral blood stem cells (PBSCs). In addition, blood in the umbilical cord contains hematopoietic cells. All of these sources of stem cells can be used in bone marrow transplants.

Bone marrow transplants are performed in cancer patients for two main reasons:

• To directly attack and kill cancer cells. Transplanted bone marrow can recognize cancer cells that exist in a patient as being abnormal, and will attack and try to destroy the cancer cells.
  
  
• To support other cancer-fighting therapies. High doses of chemotherapy or radiation therapy are often used to target and kill cancer cells. However, these treatments have the undesirable side effect of killing normal cells as well. Bone marrow cells generally are more vulnerable to these destructive effects than any other cells in the body.

Bone marrow transplants can help replace these destroyed cells that are essential to life. As a result, physicians are able to administer higher doses of chemotherapy and radiation to a patient with the knowledge that destroyed healthy cells can be replaced with a bone marrow transplant. Higher doses of these anticancer treatments increase the odds of successfully eradicating the cancer. Bone marrow transplants are not usually considered for a cancer patient unless there is evidence the patient will have a significant response to the other cancer treatments.

A transplant provides patient's bone marrow with new stem cells that can develop into cells designed to fight infections, prevent bleeding and carry oxygen to tissues. Hematopoietic cells from any source – bone marrow, bloodstream or umbilical cord – can be used in bone marrow transplantation. There are three types of transplants:

• Autologous transplant. A patient’s own stem cells are used.
  
  
• Syngeneic transplant. Stem cells from an identical twin are used. Because identical twins share the same genes, there is no risk of rejection in this form of transplant.
  
  
• Allogeneic transplant. Stem cells come from someone other than the patient or an identical twin. This can be a family member, or someone unrelated to the patient.

Bone marrow transplants are most often used in treatment of leukemia or lymphoma, and are most effective when these diseases are in remission. Other cancers that may require bone marrow transplants include neuroblastoma and multiple myeloma. Researchers also are evaluating the potential effectiveness of using bone marrow transplants in the treatment of a host of other cancers, as well as to reduce the risk of rejection following organ transplantation.

A group of specialists, known as the transplant team, are typically involved with all aspects of the bone marrow transplant. The team may include:

• Physicians who specialize in oncology, hematology, bone marrow transplants and infectious diseases
• Transplant nurses
• Dieticians
• Physical therapists
• Social workers