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.
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.