Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Childhood Non-Hodgkin Lymphoma ?
    ### Response:
    Key Points
                    - Childhood non-Hodgkin lymphoma is a disease in which malignant (cancer) cells form in the lymph system.    - The main types of lymphoma are Hodgkin lymphoma and non-Hodgkin lymphoma.    - There are three major types of childhood non-Hodgkin lymphoma.
    