5. Collect archival tumour tissue before gefitinib treatment (blood and re-biopsy tumour tissue samples are optional) ; tumor tissue samples requirements: 1) slices requirements: >1 cm2, thickness 4-5 μm, ≥ 15 slices. or, whole FFPE block; 2) tumor percentage > 20% and necrosis < 30% by pathology QC.