Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Gray zone lymphoma ?
    ### Response:
    Gray zone lymphoma is a cancer of the immune system.  The name of this lymphoma refers to the fact that cancer cells in this condition are in a "gray zone" (an uncertain category) because they appear similar to that of two other types of lymphoma, classical Hodgkin lymphoma and mediastinal large B-cell lymphoma.
    