Using DNA acquired from tumor tissue, sequencing and PNA-clamping for EGFR gene will be performed. The detection rates of EGFR mutation will be compared using paired samples.

Single arm, open label, prospective, observational study of gefitinib treatment for locally advanced (stage IIIB) or IV (metastatic) or relapsed NSCLC patients.

Using DNA acquired from tumor tissue, sequencing and PNA-clamping for EGFR gene will be performed. The detection rates of EGFR mutation will be compared using paired samples.

Inclusion Criteria:

• Locally advanced stage IIIB not suitable for curative therapy or stage IV (metastatic) disease or relapsed NSCLC
• ECOG Performance status 0~2.
• Written Informed Consent
• Female or male patients aged 18 years or over, eligible for treatment for NSCLC

Exclusion Criteria:

• Previous exposure to EGFR-TKI
• Concomitant use of other anti-cancer drugs with EGFR-TKI
• Patients without available Tumor DNA
• As judged by the investigator, any evidence of severe or uncontrolled systemic disease (e.g. unstable or uncompensated respiratory, cardiac, hepatic, or renal disease)
• Evidence of any other significant clinical disorder or laboratory finding that makes it undesirable for the subject to participate in the study
• Pregnancy or breast-feeding women (women of child¬bearing potential). Women of childbearing potential must practice acceptable methods of birth control to prevent pregnancy.

Locally advanced stage IIIB or IV (metastatic) or Relapsed Non-Small Cell Lung Cancer