Inclusion Criteria:

1. Male or female patients aged 20 years or older

2. Pathologically confirmed stage IIIB (unresectable) or IV lung adenocarcinoma

3. Documented EGFR mutation (e.g., exon 19 deletion, exon 21 L858R, etc.) with tumor
tissue

4. Patients who have 1 or more measurable lesions according to RECIST version 1.1

5. ECOG performance status 2 or less

6. Life expectancy of 12 weeks or more

7. Patients who have adequate hematological, hepatic and renal functions; WBC 4,000 or
more per mm3, platelet 100,000 or more per mm3, serum creatinine 1.5 times or less
upper limit of normal, AST and ALT 2.5 times or less upper limit of normal, total
bilirubin 1.5 times or less upper limit of normal

8. Patients who give written informed consent voluntarily

Exclusion Criteria:

1. Prior systemic chemotherapy, immunotherapy or biological therapy for stage IIIB or IV
adenocarcinoma (However, neo or adjuvant chemo, chemoradio or radiotherapy is
permitted if at least 6 months has elapsed prior to disease progression)

2. Prior treatment with small molecules or antibodies targeting EGFR

3. Patients who received major surgery within 4 weeks before study drug administration

4. Symptomatic CNS metastases (patients with radiologically and neurologically stable
metastases and being off corticosteroids for at least 2 weeks are able to participate
in this trial.)

5. History of other malignancies except effectively treated non-melanoma skin cancers,
carcinoma in situ of the cervix, ductal carcinoma in situ or effectively treated
malignancy that has been in remission for 3 years or more and considered to be cured
by investigator's judgment

6. Known preexisting interstitial lung disease (ILD)

7. NYHA class III or IV heart failure, uncontrolled hypertension, unstable angina or
myocardial infarction within 6 months, poorly controlled arrhythmia or other
clinically significant cardiovascular abnormalities at investigator's discretion

8. Patients whose left ventricle ejection fraction (LVEF) is below the institutional
lower limit of normal (if no lower limit of normal is defined in the site, the lower
limit is 50 percent)

9. Patients with known active hepatitis B, HIV infection, or other uncontrolled
infectious disease

10. Clinically significant or recent acute gastrointestinal disorders with diarrhea as a
major symptom (e.g., Crohn's disease, malabsorption disorders, CTCAE grade 2 diarrhea
or more due to any etiology)

11. Patients who cannot receive IP by mouth and be diagnosed with clinically significant
gastrointestinal disorders which can prevent administration, transit or absorption of
the study drug

12. Pregnancy or breast feeding

13. Women of childbearing potential (WOCBP) or men who are unwilling to use adequate
contraception or be abstinent during the trial and for at least 2 months after the
end of treatment

14. Patients who received other investigational products except gefitinib and erlotinib
within 4 weeks before participation

15. Patients who cannot participate in this trial by investigator's judgment