Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) chordoma ?
    ### Response:
    A chordoma is a rare type of cancerous tumor that can occur anywhere along the spine, from the base of the skull to the tailbone. Chordomas grow slowly, gradually extending into the bone and soft tissue around them. They often recur after treatment, and in about 40 percent of cases the cancer spreads (metastasizes) to other areas of the body, such as the lungs.
    