A Study of Serum Protein Profiling in Patients With Non-Small Cell Lung Cancer Treated With Gefitinib or Erlotinib

We hypothesize that Epidermal growth factor receptor tyrosine kinase inhibitors modulate tumor changes that may be reflected in the alteration of serum proteins. Study objectives are: * To establish serum proteomic changes in patients with non-small cell lung cancer (NSCLC) receiving erlotinib or gefitinib. * To identify a serum protein profile that predicts erlotinib or gefitinib sensitivity or resistance in NSCLC patients with and without EGFR mutations. * To study the toxicity of erlotinib or gefitinib by correlating clinical toxicity with serum protein profile.