A Study to Assess the Efficacy of Erlotinib for Leptomeningeal Carcinomatosis in EGFR Mutation Positive Non-small Cell Lung Cancer

Inclusion Criteria: 1. Age \>18 2. Histologically or pathologically proven non-small cell lung cancer (NSCLC) 3. Leptomeningeal carcinomatosis confirmed by CSF cytology 4. A patients with EGFR mutation (including exon 19 deletion, L858R) 5. ECOG performance status 0-3 6. Expected life time more than at least 4 weeks 7. A patients who signed the informed consent prior to the participation in the study 8. Chemotherapy-naïve patient is eligible 9. Previous EGFR TKI is allowed if this drug was not specifically used for CNS metastases Exclusion Criteria: 1. A pregnant or lactating patient 2. A patient of childbearing potential without being tested for pregnancy at baseline or with a positive test. (A postmenopausal woman with the amenorrhea period of at least 12 months or longer is considered to have non-childbearing potential.) 3. A man or woman of childbearing potential without the willingness to use a contraceptive measures during the study 4. A patient with history of another malignant disease within past 3 years, except curatively treated basal cell carcinoma of the skin, cervical carcinoma in situ, and early gastric cancer 5. A patient with active interstitial lung disease, except simple lymphangitic lung metastasis 6. A patient with history of allergic reaction to gefitinib or erlotinib 7. The following laboratory test results: * Number of absolute neutrophils counts (ANC) \< 1.0ⅹ109/L * Number of platelets \< 50 ⅹ109/L * AST, ALT \> 2.5 ⅹupper limit of normal * Total bilirubin \> 1.5 ⅹupper limit of normal * Serum creatinine \> 1.5 ⅹupper limit of normal 8. A patient with serious disease as followings * Uncontrolled cardiac arrhythmia * History of myocardial infarction within 6 months prior to the initiation of study * Neurological or psychiatric disorder including dementia or uncontrolled seizure 9. A patient who refused to sign the informed consent