The purpose of this study is to determine if TLK286(Telcyta) is more effective than gefitinib (Iressa) in the treatment of non-small cell lung cancer.
Inclusion Criteria: * Clinical diagnosis of non-small cell lung cancer * Non-small cell lung cancer that is not curable with surgery, radiation, or combined modality chemoradiation * Failed two prior chemotherapy regimens which must have included platinum * Measurable disease Exclusion Criteria: * Treatment with more than two prior chemotherapy regimens * History of bone marrow transplantation or stem cell support * Pregnant or lactating women * Known history of prior gefitinib therapy * Known history of prior TLK286 therapy