Advances in the treatment of cancer and improvements in supportive care over the past 10 years have improved the results and tolerability of blood and marrow transplants (BMT). However, BMT remains a major procedure. For allogeneic transplantation, the patient receives bone marrow or blood stem cells from a tissue-matched (HLA-matched) donor who may or may not be a relative. Identical twin allogeneic transplants are called syngeneic transplants.