Efficiency of Icotinib in Plasma ctDNA EGFR Mutation-positive Patients Diagnosed With Lung Cancer

Inclusion Criteria: * Clinical diagnosis of peripheral lung cancer, but the pathological diagnosis is not yet clear. * Plasma EGFR mutations (EGFR 19del and/or 21L858R) positive (simultaneously detected by Super-ARMS, ddPCR and NGS，any positive). * unavailable of radical surgery or radical radiotherapy. * not previously received anticancer therapy like surgery, chemotherapy, radiation therapy, and biotherapy etc. * Palliative radiotherapy for bone metastases is permitted, but there is no continuous toxicity associated with radiation therapy. * Age 18-75 years old with performance status of 0 to 3. * With a measurable disease(longest diameters \>=10mm with Spiral computed tomography (CT)) according to RECIST Criteria.None of the lesions treated with radiotherapy could be used as target lesions. * Adequate hematological, biochemical and organ functions. Exclusion Criteria: * Severe systemic disease out of control such as unstable or uncompensated respiratory,cardiac,liver,renal diseases. * Evidence of interstitial lung diseases * Evidence of any other significant clinical disorder or laboratory finding that makes it undesirable for the subject to participate in the study * Other situations researchers think not appropriate to enter the group