Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Leukemia ?
    ### Response:
    There are four common types of leukemia. They are chronic lymphocytic leukemia, chronic myeloid leukemia, acute myeloid leukemia, and acute lymphocytic leukemia. Chronic lymphocytic leukemia, chronic myeloid leukemia, and acute myeloid leukemia are diagnosed more often in older adults.
    