Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Ewing sarcoma ?
    ### Response:
    Ewing sarcoma is a cancerous tumor that occurs in bones or soft tissues, such as cartilage or nerves. There are several types of Ewing sarcoma, including Ewing sarcoma of bone, extraosseous Ewing sarcoma, peripheral primitive neuroectodermal tumor (pPNET), and Askin tumor.
    