Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Thoracic Outlet Syndrome ?
    ### Response:
    Thoracic outlet syndrome (TOS) causes pain in the shoulder, arm, and neck. It happens when the nerves or blood vessels just below your neck are compressed, or squeezed. The compression can happen between the muscles of your neck and shoulder or between the first rib and collarbone.
    