Primary lung cancer (PLC) is the most common malignant tumor in the world.PLC is generally divided into two major groups based on pathology and treatment:small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC).NSCLC accounts for 80％-85％ and the rest is SCLC.Because of the unique biological behavior of SCLC,the combination of chemotherapy and radiotherapy is mainly used,in addition to a few early cases.If no t specified,lung cancer is always regarded as NSCLC.