Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Ewing sarcoma ?
    ### Response:
    Ewing sarcoma is a malignant (cancerous) bone tumor that affects children. It can occur any time during childhood and young adulthood, but usually develops during puberty, when bones are growing rapidly. The tumor may arise anywhere in the body, usually in the long bones of the arms and legs, the pelvis, or the chest.
    