Leukemias are classified as lymphocytic – an abnormal cell growth in the marrow cells that become lymphocytes (a type of white blood cell that plays a role in the immune system) – or myeloid – an abnormal cell growth that occurs in the marrow cells that mature into red blood cells, white blood cells and platelets.

The four main subtypes of leukemia include acute lymphoblastic leukemia, or ALL; acute myeloid leukemia, or AML; chronic lymphocytic leukemia, or CLL; and chronic myeloid leukemia, or CML. Other, more rare subtypes include hair cell leukemia, chronic myelomonocytic leukemia, juvenile myelomonocytic leukemia, large granular lymphocytic leukemia, blastic plasmacytoid dendritic cell neoplasm, B-cell prolymphocytic leukemia and T-cell prolymphocytic leukemia.