Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Richter syndrome ?
    ### Response:
    Richter syndrome is a rare condition in which chronic lymphocytic leukemia (CLL) changes into a fast-growing type of lymphoma. Symptoms of Richter syndrome can include fever, loss of weight and muscle mass, abdominal pain, and enlargement of the lymph nodes, liver, and spleen.
    