A Retrospective Study About Treatment Strategy After First/Second Line EGFR-TKI Failure

Inclusion Criteria: * Patients who was confirmed stage IV (according to International Association for the Study of Lung Cancer（IASLC） TNM staging, 2009) non-small cell lung cancer (NSCLC) by histology or cytology between year 2009 to 2013, harboring EGFR mutant type (19 and/or 21 exon mutation). * Appraisable disease, that is there must be at least one lesion with the longest diameter\>10mm according to Recist 1.1 criterion (by contrast CT). * Patients who take EGFR-TKI as first/second line therapy. Exclusion Criteria: * Patients who has taken EGFR-TKI before. * Patients who take EGFR-TKI as third or more line. * Patients who take EGFR-TKI concurrent with chemotherapy or other anti-tumor drug. * The evaluated lesions has treated with radiotherapy before or concurrent with EGFR-TKI. * Patients whose EGFR expression is positive by immunochemical and/or EGFR amplification is positive by Fluorescence In Situ Hybridization(FISH), without mutation detection evidence.