Leukemia (or Blood Cancer) is a cancer of blood-forming tissues. In acute lymphocytic leukemia, a white blood cell develops errors in its DNA which cause it to multiply uncontrollably, while acute myeloid leukemia is caused by excess immature white blood cells that multiply uncontrollably. There are at least five types of leukemia: Acute lymphocytic leukemia (ALL, less commonly known as acute lymphoblastic leukemia) acute myeloid leukemia (AML, also known as acute myelocytic leukemia, or acute nonlymphocytic leukemia) chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CMML), and juvenile myelomonocytic leukemia (JMML). JMML is extremely rare.