Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) lung cancer ?
    ### Response:
    Lung cancer is a disease in which certain cells in the lungs become abnormal and multiply uncontrollably to form a tumor. Lung cancer may or may not cause signs or symptoms in its early stages. Some people with lung cancer have chest pain, frequent coughing, breathing problems, trouble swallowing or speaking, blood in the mucus, loss of appetite and weight loss, fatigue, or swelling in the face or neck.
    