This is a multi-center retrospective study, designing to access the best treatment strategy in non-small cell lung cancer (NSCLC) patients harboring EGFR mutant type after first/second line EGFR-TKI failure. The study end point is Progression Free Survival 2 (PFS2), which is defined as the time period from Progression Disease 1(PD1) to Progression Disease 2(PD2). PD1 is defined as the first tumor progression time from taking EGFR-TKI evaluated by Recist 1.1 criterion, and PD2 as the second tumor progression time after EGFR-TKI failure no matter what second/third line treatment was, PD2 is also evaluated by Recist 1.1 criterion.

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.

Patients who were diagnosed with stage IV non-small cell lung cancer (NSCLC) harboring EGFR mutant type (19 and/or 21 exon mutation), and took EGFR-TKI as first/second line therapy.