The T790M mutation is highly sensitive to osimertinib, which is approved in this setting following failure of gefitinib, erlotinib or afatinib. In contrast to first- and second-generation EGFR TKIs, no predominant resistance mechanism to first-line osimertinib has been clearly defined yet. The most common mechanisms of resistance were c-MET amplification only for 15% of patients and the emergence of the EGFR C797S mutation in 7%, while > 60% of patients were still with no identifiable mechanisms of resistance. As a result, targeted treatment options following first-line osimertinib failure remain limited. Thus, interest on sequential administration of EGFR TKIs in patients with EGFR mutation-positive NSCLC has been growing. So, here in this study, we intend to investigate treatment outcome (TOT) along with the several treatment options starting from the first line EGFR TKI treatment to various second line treatments including 3rd generation TKI and chemotherapy and others.

Inclusion Criteria:

1. Age more than 18 years
2. Stage IIIB/IIIC/IV/IVA/IVB NSCLC patients treated with first-line afatinib for EGFR sensitizing mutations (Del19, L858R, G719X, S768I, or L861Q etc.)
3. Afatinib treatment was started 13 month prior to data collection date to reduce premature censoring of patients. Data cutoff date will be determined before data entry starts.

Exclusion Criteria:

1. Patients who received drug(s) other than afatinib (Giotrif®) as the first-line treatment
2. Patients who received drug(s) other than 3rd-generation EGFR TKI osimertinib as the second-line in "Cohort A'

non-interventional, multi-center, multi-cohort