Leukemia also spelled leukaemia, is cancer of the body's blood-forming tissues, including the bone marrow and the lymphatic system. Leukemia is a group of blood cancers that usually result in high numbers of abnormal blood cells. Many types exist such as acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and chronic lymphocytic leukemia (CLL) and chronic myeloid leukemia (CML).