Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Castleman disease ?
    ### Response:
    Castleman disease (CD) is a rare condition that affects the lymph nodes and related tissues. There are two main forms: unicentric CD and multicentric CD. Unicentric CD is a "localized" condition that is generally confined to a single set of lymph nodes, while multicentric CD is a "systemic" disease that affects multiple sets of lymph nodes and other tissues throughout the body.
    