2. Stable disease >=6 months as defined by RECIST in absence of radiographic progression after initiation of gefitinib or erlotinib; or stable disease/PR/CR >=12 weeks as defined by RECIST after initiation of BIBW 2992 3. Systemic progression of disease (RECIST v1.1) while on continuous treatment with erlotinib or gefitinib or BIBW 2992 within the last 30 days. Patients whose disease progresses only in the central nervous system (CNS) are not eligible 4. No intervening systemic therapy between cessation of gefitinib or erlotinib or BIBW 2992 and initiation of the treatment in the study 5. Adequate tumor-derived material such as fresh or archived tumor tissue or pleural fluid from malignant pleural effusion after disease progression on erlotinib/gefitinib/BIBW 2992 prior to the study entry must be made available for EGFR mutation analyses 6. Patients aged 18 years or older 7. Life expectancy of at least three (3) months 8. Eastern Cooperative Oncology Group (ECOG) performance score 0-2 9. Written informed consent that is consistent with ICH-GCP guidelines