This multicenter, retrospective and prospective observational, cohort study will examine the effect of second-line Tarceva treatment on long response in non-small cell lung cancer (NSCLC) participants with wild type or unknown EGFR status. Participants will be observed from the start of treatment for 8 months or until death. The extension of the retrospective versus prospective observation will depend on the lag between the date of the participant enrollment and the date of beginning of erlotinib therapy.