Then these donors undergo a process called apheresis, a four-to-six-hour process in which blood is removed through a large vein in the art, neck, chest or groin and put through a machine to pull out the stem cells.
No matter how the stem cells are harvested, the recipient is first treated with high-dose anticancer drugs and/or radiation, and then receives the donor cells through an intravenous infusion.
Appelbaum said about 5,500 unrelated donor transplants were performed in the United States last year. More than 20 million unrelated donors are typed and listed in registries in North and South America, Europe and Asia.
The large, multicenter, randomized trial compared survival rates and side effects of treating people with either hematopoietic (blood-forming) adult stem cells obtained from bone marrow or adult stem cells derived from circulating blood.
Between March 2004 and September 2009, the researchers enrolled 551 patients at 48 centers. Patients were randomly assigned to receive either peripheral blood stem cell or to bone marrow transplantation, based partially on their disease risk and transplantation center. The average follow-up of surviving patients was at 36 months.
In addition to showing no survival difference between transplant recipients who received bone marrow or peripheral stem cells, the study showed no difference in relapse rates, mortality unrelated to relapse or rate of acute GVHD.
Those who received peripheral blood transplants had better engraftment -- the process of transplanted cells producing new cells -- and the bone marrow transplant patients experienced less extensive chronic GVHD.
Appelbaum said that the results of the study should change practice. For most unrelated donor transplants, bone marrow rather than peripheral blood should be the first choice, he argued. But he's unsure whether it will.
"The benefits of peripheral blood are seen early, under the watchful eyes of the transplant physician, while the deleterious effects occur late, often after the patient has left the transplant center," his editorial concluded.
Learn more about bone marrow and peripheral blood cell transplantation from the U.S. National Cancer Institute.
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