Leukemia is a cancer of the white blood cells that spreads throughout the bloodstream and may affect many organs. It originates in the bone marrow (spongy center of bones), which is where all blood cells are developed before being released into the bloodstream. Leukemia is classified based on the type of abnormal white blood cell and by how rapidly these cells leave the bone marrow and enter the bloodstream. Acute myeloid leukemia (AML) is the most common type of leukemia that affects adults. The December 22/29, 2010, issue of JAMA includes an article about the association between genetic characteristics of leukemia cells and outcomes of the disease. This Patient Page is based on one published in the June 10, 2009, issue of JAMA.