Inclusion Criteria:  Age more than 18 years Stage IIIB/IIIC/IV/IVA/IVB NSCLC patients treated with first-line afatinib for EGFR sensitizing mutations (Del19, L858R, G719X, S768I, or L861Q etc.) 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:  Patients who received drug(s) other than afatinib (Giotrif®) as the first-line treatment Patients who received drug(s) other than 3rd-generation EGFR TKI osimertinib as the second-line in "Cohort A'