Carcinoma, Non-Small-Cell Lung/drug therapy; Carcinoma, Non-Small-Cell Lung/genetics; Lung Neoplasms/drug therapy; Lung Neoplasms/genetics; Protein-Tyrosine Kinases/genetics; Quinazolines/administration & dosage; Aged; Biopsy, Needle; Blotting, Western; Carcinoma, Non-Small-Cell Lung/mortality; Cohort Studies; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; ErbB Receptors/antagonists & inhibitors; Female; Gefitinib; Gene Expression Regulation, Neoplastic/drug effects; Humans; Immunohistochemistry; In Situ Hybridization, Fluorescence; Kaplan-Meier Estimate; Lung Neoplasms/mortality; Male; Middle Aged; Multivariate Analysis; Mutation/drug effects; Neoplasm Staging; Probability; Proportional Hazards Models; Protein Kinase Inhibitors/administration & dosage; Protein-Tyrosine Kinases/drug effects; Survival Analysis; Treatment Outcome