Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Chronic Myeloid Leukemia ?
    ### Response:
    Leukemia is cancer of the white blood cells. White blood cells help your body fight infection. Your blood cells form in your bone marrow. In leukemia, the bone marrow produces abnormal white blood cells. These cells crowd out the healthy blood cells, making it hard for blood to do its work.
    