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.

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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.