['non-small cell lung cancer']
['gefitinib']

        Inclusion Criteria:

          -  Histologically confirmed stage IIIB/IV or recurrent NSCLC with activating EGFR
             mutation in exon 18 through exon 21 except T790M

          -  Patients who achieved complete/partial response more than 4 months or stable disease
             more than 6 months with first-line or second line gefitinib

          -  Patients who experience disease progression by RECIST 1.1 criteria

          -  Age ≥ 18years

          -  ECOG performance status of 0 to 2

          -  Adequate organ function as evidenced by the following; Absolute neutrophil count > 1.5
             x 109/L; platelets > 100 x 109/L; total bilirubin ≤1.5 UNL; AST and/or ALT < 5 UNL,
             CCr ≥ 50mL/min

          -  Baseline adverse event of gefitinib ≤ Grade 2

          -  Written informed consent form

        Exclusion Criteria:

          -  Prior treatment with EGFR TKI

          -  Patients who required dose reduction of gefitinib

          -  Surgery undertaken less than 4 weeks before the study

          -  Localized radiotherapy unless completed more than 2 weeks before the study

          -  Uncontrolled systemic illness such as DM, CHF, unstable angina, hypertension or
             arrhythmia

          -  Pregnant or nursing women ( Women of reproductive potential have to agree to use an
             effective contraceptive method (hormonal or barrier methods))

          -  Uncontrolled symptomatic brain metastasis

          -  Prior history of malignancy within 5 years from study entry except for adequately
             treated basal cell or squamous cell skin cancer or in situ cervical cancer,
             well-treated thyroid cancer

          -  Concomitant use of CYP3A4 inducers/inhibitors

          -  Prolonged QT interval in ECG (QTc >450 msec)

          -  Patients who cannot take a medicine orally or who have a gastrointestinal absorption
             disorder
      